CN111142090A - Laser altimeter cloud scattering error correction method and device - Google Patents
Laser altimeter cloud scattering error correction method and device Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/487—Extracting wanted echo signals, e.g. pulse detection
- G01S7/4873—Extracting wanted echo signals, e.g. pulse detection by deriving and controlling a threshold value
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
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Abstract
The invention provides a laser altimeter cloud scattering error correction method and device, wherein the method comprises the following steps: acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers of different altitudes; calculating original height measurement data according to the echo waveform data; calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power; calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient; calculating a weakening coefficient according to the backscattering coefficient and the extinction coefficient; calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient; calculating a height measurement deviation correction value according to a height measurement deviation model caused by cloud optical thickness and atmospheric scattering; and calculating and correcting the height measurement data according to the original height measurement data and the height measurement deviation correction value. By the method, the height measurement deviation correction value can be rapidly calculated, and the calculated height measurement deviation correction value is accurate.
Description
Technical Field
The invention relates to the technical field of satellite laser height measurement, in particular to a method and a device for correcting cloud scattering errors of a laser height measuring instrument.
Background
Satellite laser height measurement is a technology capable of acquiring sub-meter or even centimeter-level elevation information in a high-frequency and large-range manner, and becomes one of important means for earth observation. However, when clouds exist in the atmosphere, laser pulses are stretched due to the influence of multiple scattering and absorption of the clouds, so that the receiving time of the pulse centroid is subjected to deviation measurement and delay when the pulse centroid is received, and therefore when the height is measured through satellite laser, the clouds are a non-negligible factor in order to guarantee the elevation accuracy of acquired data. Based on the finding, the researcher simulates the influence of cloud multiple scattering on the laser height measurement data precision under specific conditions based on a semi-resolution Monte Carlo method, and the result shows that the height measurement deviation is related to various factors such as cloud layer height, cloud effective particle radius, cloud optical thickness and concentration, so that the height measurement deviation must be corrected based on real-time atmospheric observation parameters and the semi-resolution Monte Carlo method to improve the distance measurement value. However, in actual observation, it is difficult to synchronously acquire real-time atmospheric related data, the correction of the height measurement result cannot be quickly completed, and the correction precision is low.
Disclosure of Invention
Therefore, the technical problem to be solved by the present invention is to overcome the defect in the prior art that the height measurement result cannot be corrected quickly, so as to provide a method and a device for correcting the cloud scattering error of a laser height indicator.
The invention provides a method for correcting cloud scattering errors of a laser altimeter, which comprises the following steps: acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers of different altitudes; calculating original height measurement data according to the echo waveform data; calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power; calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient; calculating a weakening coefficient according to the backscattering coefficient and the extinction coefficient; calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient; calculating a height measurement deviation correction value according to a height measurement deviation model caused by cloud optical thickness and atmospheric scattering; and calculating and correcting the height measurement data according to the original height measurement data and the height measurement deviation correction value.
Optionally, the step of calculating the backscattering coefficient and extinction coefficient at different altitudes according to the echo power comprises: calculating the temperature, the air pressure and the relative humidity at different altitudes according to the echo power and a preset temperature function, a preset air pressure function and a preset relative humidity function at different altitudes; calculating backscattering coefficients at different altitudes according to the temperature, the air pressure and the relative humidity at different altitudes; and calculating extinction coefficients at different altitudes according to the backscattering coefficients.
Optionally, calculating the cloud top height from the backscatter coefficients comprises: calculating top threshold values at different altitudes according to backscattering coefficients at different altitudes and a preset scattering constant; and determining the altitude corresponding to the first backscattering coefficient larger than the top threshold as the cloud top height.
Optionally, the top threshold is calculated by the following formula: t ist＝(βm(z) + ψ). F, wherein, βmA backscatter coefficient indicating a current altitude, Ψ denotes a scattering constant, F ═ 0.70d0+ (i _ bin _ cnt/2)/180.0d0), i _ bin _ cnt denotes a node number of the current altitude, and d0 denotes that echo power received by the laser altimeter is converted into a quantized value between 0 and 255.
Optionally, calculating the cloud base height from the backscattering coefficient comprises: calculating bottom thresholds at different altitudes according to backscattering coefficients at different altitudes, cloud top heights, node numbers of the cloud top heights and top thresholds corresponding to the cloud top heights; and determining the altitude corresponding to the first backscattering coefficient larger than the bottom threshold as the cloud bottom height.
Optionally, the bottom threshold is calculated by the following formula: t isb＝Tt- (i _ bin _ cnt-i _ bin _ top) · d _ top _ thr · 0.0010, wherein i _ bin _ top represents a node number of the current cloud top height, and d _ top _ thr represents a top threshold corresponding to the current cloud top height.
Optionally, the cloud optical thickness is calculated by the following formula:
wherein z istopDenotes the height of the cloud ceiling, zbottomDenotes the height of the cloud base, Sα(z) represents the attenuation coefficient at altitude z.
Optionally, the model of altimetry deviation caused by atmospheric scattering is: y ═ a + b · Exp (c · τ), where τ denotes the cloud optical thickness.
The invention provides a laser altimeter cloud scattering error correcting device in a second aspect, which comprises: the echo waveform data acquisition module is used for acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers of different altitudes; the original height measurement data calculation module is used for calculating original height measurement data according to the echo waveform data; the backscattering coefficient calculation module is used for calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power; the cloud detection module is used for calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient; the attenuation coefficient calculation module is used for calculating an attenuation coefficient according to the backscattering coefficient and the extinction coefficient; the cloud optical thickness calculating module is used for calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient; the height measurement deviation correction value calculation module is used for calculating a height measurement deviation correction value according to a height measurement deviation model caused by cloud optical thickness and atmospheric scattering; and the corrected height measurement data calculation module is used for calculating corrected height measurement data according to the original height measurement data and the height measurement deviation correction value.
A third aspect of the present invention provides a computer apparatus comprising: at least one processor; and a memory communicatively coupled to the at least one processor; the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so as to execute the laser altimeter cloud scattering error correction method according to the first aspect of the present invention.
A fourth aspect of the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the method for correcting cloud scattering error of a laser altimeter according to the first aspect of the present invention.
The technical scheme of the invention has the following advantages:
1. the invention provides a method for correcting cloud scattering errors of a laser altimeter, which comprises the steps of obtaining echo waveform data of altimeter laser, calculating original altimeter data according to the echo waveform data, then calculating backscattering coefficients and extinction coefficients of the laser at different altitudes according to the echo waveform data, calculating cloud top height and cloud bottom height of a cloud layer according to the backscattering coefficients, calculating weakening coefficients according to the backscattering coefficients and the extinction coefficients, calculating cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficients, finally calculating a height correction value according to the cloud optical thickness and a preset height correction value calculation model, obtaining corrected height measurement data according to the height correction value and the original height measurement data, and according to the processes, the calculation is carried out only based on the acquired echo waveform data of the altimetry laser without acquiring other parameters, so that the calculation process is simple, corrected altimetry data can be quickly acquired, and the cloud optical thickness is the main factor of the laser altimetry result error, so that the calculated cloud optical thickness is substituted into an altimetry deviation model caused by atmospheric scattering, the altimetry deviation correction value can be quickly calculated, and the calculated altimetry deviation correction value is accurate.
2. According to the cloud scattering error correction method for the laser altimeter, when the cloud top height is calculated, the backscattering coefficients and the top threshold values at different altitude positions are calculated respectively, and when the backscattering coefficient of a certain height is larger than the top threshold value, the height is judged to be the cloud top height. Because the cloud layer and different altitudes cause different backscattering coefficients of laser, the backscattering coefficients and the top threshold value at different altitudes are respectively calculated, the altitude corresponding to the first backscattering coefficient larger than the top threshold value is determined as the cloud top height, and the cloud layer influencing the height measurement data can be accurately and quickly found.
3. According to the cloud scattering error correction method of the laser altimeter, provided by the invention, after the cloud top height is obtained through calculation, the backscattering coefficients and the bottom threshold value at different altitude positions are respectively calculated when the cloud bottom height is calculated, and when the backscattering coefficient of a certain height is larger than the top threshold value, the height is judged to be the cloud bottom height. The cloud layer and different altitudes cause different backscattering coefficients of the laser, so the backscattering coefficients and the bottom threshold at different altitudes are calculated respectively, the altitude corresponding to the first backscattering coefficient larger than the bottom threshold is determined as the cloud bottom height, and the cloud layer influencing the height measurement data can be accurately and quickly found.
4. The invention provides a cloud scattering error correction device of a laser altimeter, which obtains echo waveform data of altimeter laser, calculates original altimeter data according to the echo waveform data, calculates backscattering coefficients and extinction coefficients of the laser at different altitudes according to the echo waveform data, calculates cloud top height and cloud bottom height of a cloud layer according to the backscattering coefficients, calculates weakening coefficients according to the backscattering coefficients and the extinction coefficients, calculates cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficients, calculates a height measurement correction value according to the cloud optical thickness and a preset height measurement correction value calculation model, and can obtain corrected height measurement data according to the height measurement correction value and the original height measurement data, the calculation is carried out only based on the acquired echo waveform data of the altimetry laser without acquiring other parameters, so that the calculation process is simple, corrected altimetry data can be quickly acquired, and the cloud optical thickness is the main factor of the laser altimetry result error, so that the calculated cloud optical thickness is substituted into an altimetry deviation model caused by atmospheric scattering, the altimetry deviation correction value can be quickly calculated, and the calculated altimetry deviation correction value is accurate.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a flowchart illustrating a specific example of a method for correcting cloud scattering errors of a laser altimeter according to an embodiment of the present invention;
FIG. 2 is a graph of echo power obtained in an embodiment of the present invention;
3-4 are flowcharts illustrating a specific example of a method for correcting cloud scattering error of a laser altimeter according to an embodiment of the present invention;
FIG. 5 is a diagram illustrating data distribution and a corrected model distribution of the Sinkiang lake region according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of a laser altimeter cloud scattering error correction device in an embodiment of the present invention;
FIG. 7 is a diagram of a computer device according to an embodiment of the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The technical features mentioned in the different embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.
Example 1
Satellite laser height measurement is a technology capable of acquiring sub-meter or even centimeter-level elevation information in a high-frequency and large-range manner, and becomes one of important means for earth observation. When the height is measured by satellite laser, cloud is a non-negligible factor in order to ensure the elevation accuracy of the acquired data. Based on the finding, the researcher simulates the influence of cloud multiple scattering on the laser height measurement data precision under specific conditions based on a semi-resolution Monte Carlo method, and the result shows that the height measurement deviation is related to various factors such as cloud layer height, cloud effective particle radius, cloud optical thickness and concentration, so that the height measurement deviation must be corrected based on real-time atmospheric observation parameters and the semi-resolution Monte Carlo method to improve the distance measurement value. However, in actual observation, it is difficult to synchronously acquire real-time atmospheric related data, the correction of the height measurement result cannot be quickly completed, and the correction precision is low.
The embodiment of the invention provides a laser altimeter cloud scattering error correction method, as shown in fig. 1, comprising the following steps:
step S10: and acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers at different altitudes, and the echo powers at different altitudes are shown in figure 2.
Step S20: the raw altimetry data is calculated from the echo waveform data using conventional calculation methods, such as time-centroid method.
Step S30: and calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power, wherein the backscattering coefficients represent the influence of atmospheric environment on laser pulses in atmospheric transmission, and the influence generally refers to the scattering action of atmospheric particles such as clouds and the like.
Step S40: and calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient. The difference of the number of cloud particles existing at different altitudes can cause the difference of backscattering coefficients, so that the cloud top height and the cloud bottom height can be calculated according to the backscattering coefficients.
Step S50: and calculating the weakening coefficient according to the backscattering coefficient and the extinction coefficient.
Step S60: and calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient.
In a specific embodiment, the cloud optical thickness is calculated by a slope method, because the backscattering signals generated by interaction with laser pulses in the atmosphere include particle scattering influences such as atmospheric molecules and clouds, the two scattering influences belong to rayleigh scattering and meter scattering respectively, the intensity of the rayleigh scattering signals is proportional to the-4 th power of the radiation wavelength, the intensity of the meter scattering signals is proportional to the- (1-2) th power of the radiation wavelength, and under the condition of longer wavelength or higher cloud density, the meter scattering signals in the atmospheric echo signals occupy main components, while the rayleigh scattering signals are relatively weak and can be ignored.
When the cloud optical thickness is calculated by a slope method, firstly, a weakening coefficient is calculated according to a backscattering coefficient and an extinction coefficient, and a calculation formula is shown as a formula (1):
Sα(z)＝αα(z)βα(z)， (1)
wherein z is the altitude of the laser pulse, Sα(Z) is the cloud attenuation coefficient (also known in some literature as the effective extinction coefficient) for the laser, representing the total energy scattered at the Z height, βα(z) backscattering coefficient of cloud, αα(z) is the extinction coefficient of the cloud.
Then, the cloud optical thickness is calculated according to the cloud top height, the cloud bottom height and the weakening coefficient, and the calculation formula is shown as the formula (2):
wherein τ is cloud opticsThickness, ztopIs the height of the cloud ceiling, zbottomIs the height of the cloud base.
Step S70: and calculating a height measurement deviation correction value according to the cloud optical thickness and the height measurement deviation model.
Step S80: and calculating and correcting the height measurement data according to the original height measurement data and the height measurement deviation correction value. In experiments, it is found that large height measurement deviation can be caused by front and back scattering caused by cloud, so that the elevation of the earth surface calculated by a time-gravity-center method is small, error correction can be completed by adding a height measurement deviation correction value calculated by a correction model to the original height measurement data, and the obtained corrected height measurement data is more accurate height measurement data.
The method for correcting the cloud scattering error of the laser altimeter, provided by the embodiment of the invention, comprises the steps of obtaining echo waveform data of altimeter laser, calculating original altimeter data according to the echo waveform data, then calculating backscattering coefficients and extinction coefficients of the laser at different altitudes, calculating cloud top height and cloud bottom height of a cloud layer according to the backscattering coefficients, calculating weakening coefficients according to the backscattering coefficients and the extinction coefficients, calculating cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficients, finally calculating a height correction value according to the cloud optical thickness and a preset height correction value calculation model, obtaining corrected height measurement data according to the height correction value and the original height measurement data, the calculation is carried out only based on the acquired echo waveform data of the altimetry laser without acquiring other parameters, so that the calculation process is simple, corrected altimetry data can be quickly acquired, and the cloud optical thickness is the main factor of the laser altimetry result error, so that the calculated cloud optical thickness is substituted into an altimetry deviation model caused by atmospheric scattering, the altimetry deviation correction value can be quickly calculated, and the calculated altimetry deviation correction value is accurate.
In a specific embodiment, there may be more than one layer of cloud in the altimetric atmosphere, when there are multiple layers of clouds, the cloud top height and the cloud bottom height of each layer of cloud need to be calculated respectively, then the cloud optical thickness of each layer of cloud needs to be calculated respectively, the calculated multiple cloud optical thicknesses are substituted into an altimetric deviation model caused by atmosphere scattering respectively, multiple altimetric deviation correction values are calculated, and then all the altimetric deviation correction values are added to the original altimetric data to obtain corrected altimetric data.
In an alternative embodiment, as shown in fig. 3, step S30 specifically includes:
step S31: and calculating the temperature, the air pressure and the relative humidity at different altitudes according to the echo power and the preset temperature function, the preset air pressure function and the preset relative humidity function at different altitudes. In a specific embodiment, the preset temperature function, the preset air pressure function and the preset relative humidity function at different altitudes can be obtained by querying an american standard atmospheric table, the temperature, the air pressure and the relative humidity at different altitudes can be calculated through the echo power, and the echo power changes suddenly when clouds exist in the atmosphere, as shown in fig. 2, when the detected altitude is c, the signal intensity changes suddenly, so that the existence of cloud particles can also affect the temperature, the air pressure and the relative humidity of the atmosphere at the same altitude.
Step S32: and calculating the backscattering coefficients at different altitudes according to the temperature, the air pressure and the relative humidity at different altitudes. The backscattering coefficient is a physical quantity related to the laser pulse wavelength (1064nm) and the height of the pulse. The calculation formula of the backscattering coefficient is shown in formula (3):
βm(z,λ)＝5.45N(z)(550/λ)410-26， (3)
therein, βmFor the backscattering coefficient, Z is the altitude of the location, λ is the lidar wavelength (1064nm), and n (Z) is the atmospheric molecular density at altitude Z, calculated by the following equation (4):
N(z)＝P(z)/(kTv(z))， (4)
where k is the boltzmann constant of the dry air, P (z) is the atmospheric pressure at altitude z, TvIs the virtual temperature. T isvFrom relative humidity (obtained from MET data)Calculated, it is first converted to a water-vapor mixing ratio. Therefore, it is necessary to first calculate the saturation vapor pressure (es), which is a function of the atmospheric temperature (T), as shown in the following equation (5):
es＝0.612e17.67T/(T-29.66)， (5)
t is the temperature at altitude z.
The saturation mixing ratio (q) is then calculated by the following formula (6)s)：
qs＝0.622es/(p/10)， (6)
Wherein P is atmospheric pressure.
The actual atmospheric water vapor mixture ratio q is defined as the product of the relative humidity and the saturated mixture ratio divided by 100, i.e.:
q＝rqs/100， (7)
wherein qs is a saturation mixing ratio, r is relative humidity, and a virtual temperature TvCalculated by equation (8):
step S33: and calculating extinction coefficients at different altitudes according to the backscattering coefficients.
The extinction coefficient has important significance for inverting the cloud optical thickness parameter. The calculation formula (9) is as follows:
αm(z)＝Smβm(z)， (9)
wherein S ismβ for backscatter lidar ratiom(z) is the backscattering coefficient at altitude z, αm(z) is an extinction coefficient. In the embodiment of the invention, in order to better realize automatic inversion, 17.8 is used as a backscattering laser radar specific constant and is substituted into a formula to calculate the extinction coefficient.
In an alternative embodiment, as shown in fig. 4, the step of calculating the cloud top height according to the backscatter coefficients in step S40 includes:
step S41: the top threshold values at different altitudes are calculated according to the backscattering coefficients at different altitudes and the preset scattering constant, the backscattering coefficients are different due to different altitudes, and therefore different top threshold values need to be calculated for different altitudes when the cloud top height is calculated.
Step S42: and determining the altitude corresponding to the first backscattering coefficient larger than the top threshold as the cloud top height.
The process of calculating the Cloud top height is actually a process of searching for a Cloud, and in the embodiment of the invention, an algorithm adopted by a Global Laser Altimetry System (GLAS) carried on an ICESat (Ice, Cloud and land Elevation Satellite) Satellite is referred to for a Cloud search algorithm. GLAS 1064nm channel only downloads backscatter profile data in the range of 0.25km to 20km from the earth's surface, divided into sections (Bin) every 76.8 m. If the backscatter signals of three consecutive bins are greater than the threshold, then the cloud is considered to be present at that height. And then further judging the height of the cloud top and the height of the cloud bottom. In actual data processing, the influence of clouds of different heights on the laser pulse is different, so that the backscatter coefficient threshold values of different heights are calculated by iteration.
According to the cloud scattering error correction method for the laser altimeter, provided by the embodiment of the invention, when the cloud top height is calculated, the backscattering coefficients and the top threshold value at different altitude positions are respectively calculated, and when the backscattering coefficient of a certain height is larger than the top threshold value, the height is judged to be the cloud top height. Because the cloud layer and different altitudes cause different backscattering coefficients of laser, the backscattering coefficients and the top threshold value at different altitudes are respectively calculated, the altitude corresponding to the first backscattering coefficient larger than the top threshold value is determined as the cloud top height, and the cloud layer influencing the height measurement data can be accurately and quickly found.
In an alternative embodiment, the top threshold is calculated by the following equation (10):
Tt＝(βm(z)+ψ)·F， (10)
wherein the content of the first and second substances,βma backscatter coefficient indicating a current altitude, Ψ denotes a scattering constant, F ═ 0.70d0+ (i _ bin _ cnt/2)/180.0d0), i _ bin _ cnt denotes a node number of the current altitude, d0 denotes a quantized value in which echo power received by the laser altimeter is converted into a value between 0 and 255, wherein the quantized value is 0 when the echo power is 54.47, where d0 denotes the quantized value, which is numerically equivalent to 54.47. In one embodiment, taking the satellite counting from 20km above the ground, knowing that 260m above the ground ends, i _ bin _ cnt counts at 20km as 0, signals are tested starting from 19km above the ground (i _ bin _ cnt ═ 14), and moving downward, and if 3 signals occur consecutively exceeding the top threshold (Tt) corresponding to the respective altitude, it is determined that cloud interference occurs. Once this occurs, the cloud top height is defined as the height at which the first of the three nodes exceeds the threshold.
In an alternative embodiment, as shown in fig. 4, the step of calculating the cloud base height according to the backscatter coefficients in step S40 includes:
step S43: the bottom thresholds at different altitudes are calculated according to backscattering coefficients, cloud top heights, node numbers of the cloud top heights and top thresholds corresponding to the cloud top heights, the backscattering coefficients are different due to the fact that the backscattering coefficients are different when the cloud top heights are calculated and the backscattering coefficients are different when the cloud top heights are different from the backscattering coefficients, and therefore the bottom thresholds need to be calculated for the different altitudes respectively.
Step S44: and determining the altitude corresponding to the first backscattering coefficient larger than the bottom threshold as the cloud bottom height.
According to the cloud scattering error correction method for the laser altimeter, provided by the embodiment of the invention, after the cloud top height is obtained through calculation, the backscattering coefficients and the bottom threshold values at different altitudes are respectively calculated when the cloud bottom height is calculated, and when the backscattering coefficient of a certain height is larger than the top threshold value, the height is judged to be the cloud bottom height. The cloud layer and different altitudes cause different backscattering coefficients of the laser, so the backscattering coefficients and the bottom threshold at different altitudes are calculated respectively, the altitude corresponding to the first backscattering coefficient larger than the bottom threshold is determined as the cloud bottom height, and the cloud layer influencing the height measurement data can be accurately and quickly found.
In an alternative embodiment, the bottom threshold is calculated by equation (11) as follows:
Tb＝Tt-(i_bin_cnt-i_bin_top)·d_top_thr·0.0010， (11)
the i _ bin _ top represents a node number of the current cloud layer cloud top height, and the d _ top _ thr represents a top threshold corresponding to the current cloud layer cloud top height. In one embodiment, TbT initially equal to the layer toptAnd drops by about 1% per 750m range when moving downward within Bin. When the backscattering coefficient calculated by the new 3 continuous bins is found to be larger than the bottom threshold value at the respective altitude, the first Bin is judged as the bottom of the cloud layer.
To search for all clouds in the atmosphere, the search algorithm continues to define a new T according to equation (10)tUntil a new cloud is found or 250 meters above sea level (considered to be at the surface, not mixed with surface signals).
In an alternative embodiment, the model of the altimetric deviation caused by atmospheric scattering is the following equation (12):
Y＝a+b·Exp(c·τ)， (12)
where τ represents the cloud optical thickness.
The inventor of the present application finds, by studying actual data, that, for satellite laser height measurement data affected by cloud scattering, when the cloud optical thickness is less than 2, the cloud optical thickness (COD) of the data has a strong correlation with height measurement deviation caused by cloud, and the whole data has an exponential function distribution with e as a base, so that the established model of height measurement deviation caused by atmospheric scattering is an exponential function, and parameters a, b, and c in the model of height measurement deviation caused by atmospheric scattering can be obtained according to actual tests, in the embodiment of the present invention, the model of height measurement deviation caused by atmospheric scattering obtained by the inventor through experiments is formula (13):
Y＝-0.2758+0.2311*Exp(1.6153*X)。 (13)
in a specific embodiment, a height measurement deviation model caused by atmospheric scattering provided by the embodiment of the present invention is subjected to a related precision verification experiment through ICESat/GLAS data of the fegkai lake area, as shown in fig. 5, a dotted line is a deviation value between original height measurement data obtained by a conventional height measurement method and an actual height of the fegkai lake area under the influence of clouds, a smooth curve is a height measurement deviation correction value calculated by the height measurement deviation model caused by atmospheric scattering provided by the embodiment of the present invention, it can be seen from the figure that the height measurement deviation correction value is relatively consistent with the deviation value, therefore, more accurate corrected height measurement data can be obtained by adding the height measurement deviation correction value on the basis of the original height measurement data, and through calculation, when COD is 0-2, the overall Root Mean Square Error (RMSE) is 0.054, and the height measurement deviation can be corrected to within 5cm, therefore, the height measurement deviation model caused by atmospheric scattering provided by the embodiment of the invention is reliable, and the height measurement deviation correction value calculated by the model is accurate.
In a specific embodiment, when the cloud optical thickness is greater than 2, the correlation between the COD and the corresponding height measurement deviation begins to decrease, and at this time, the height measurement deviation far exceeds the precision of a standard height measurement product by 1-2 orders of magnitude, so that when the calculated COD is greater than 2, the calculated height measurement data error is too large to be corrected, and the calculated height measurement data error should be marked as that atmospheric scattering is very obvious and data quality degradation is serious, and the laser point is not recommended to be used.
Example 2
An embodiment of the present disclosure provides a laser altimeter cloud scattering error correction device, as shown in fig. 5, including:
the echo waveform data acquiring module 10 is configured to acquire echo waveform data of the altimetry laser, where the echo waveform data includes echo powers at different altitudes, and the detailed description is described in the above embodiment 1 for step S10.
The raw altimeter data calculation module 20 is configured to calculate raw altimeter data according to the echo waveform data, and the detailed description is described in the above embodiment 1 for step S20.
A backscattering coefficient calculating module 30 for calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power, which is described in detail in the above embodiment 1 for the step S30.
The cloud detection module 40 is configured to calculate a cloud top height and a cloud bottom height according to the backscatter coefficient, which is described in detail in the above embodiment 1 for the step S40.
The attenuation coefficient calculation module 50 is used for calculating the attenuation coefficient according to the backscattering coefficient and the extinction coefficient, and the detailed description is given in the above embodiment 1 for the description of step S50.
The cloud optical thickness calculating module 60 is configured to calculate the cloud optical thickness according to the cloud top height, the cloud bottom height, and the weakening coefficient, which is described in detail in the above embodiment 1 for the step S60.
The altimetry deviation correction value calculation module 70 is configured to calculate an altimetry deviation correction value according to an altimetry deviation model caused by cloud optical thickness and atmospheric scattering, which is described in detail in the above embodiment 1 for the description of step S70.
A corrected altimeter data calculation module 80 for calculating corrected altimeter data according to the original altimeter data and the altimeter deviation correction value, as described in detail in the above embodiment 1 for step S80.
The cloud scattering error correction device for the laser altimeter, provided by the embodiment of the invention, is used for obtaining echo waveform data of altimeter laser, calculating original altimeter data according to the echo waveform data, then calculating backscattering coefficients and extinction coefficients of the laser at different altitudes according to the echo waveform data, calculating cloud top height and cloud bottom height of a cloud layer according to the backscattering coefficients, calculating weakening coefficients according to the backscattering coefficients and the extinction coefficients, calculating cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficients, finally calculating a height measurement correction value according to the cloud optical thickness and a preset height measurement correction value calculation model, and obtaining corrected height measurement data according to the height measurement correction value and the original height measurement data, the calculation is carried out only based on the acquired echo waveform data of the altimetry laser without acquiring other parameters, so that the calculation process is simple, corrected altimetry data can be quickly acquired, and the cloud optical thickness is the main factor of the laser altimetry result error, so that the calculated cloud optical thickness is substituted into an altimetry deviation model caused by atmospheric scattering, the altimetry deviation correction value can be quickly calculated, and the calculated altimetry deviation correction value is accurate.
Example 3
The present invention also provides a computer device, as shown in fig. 6, the computer device mainly includes one or more processors 91 and a memory 92, and fig. 6 takes one processor 91 as an example.
The computer device may further include: an input device 99 and an output device 94.
The processor 91, the memory 92, the input device 99 and the output device 94 may be connected by a bus or other means, as exemplified by the bus connection in fig. 6.
The processor 91 may be a Central Processing Unit (CPU). The Processor 91 may also be other general purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs) or other Programmable logic devices, discrete Gate or transistor logic devices, discrete hardware components, or any combination thereof. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like. The memory 92 may include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required for at least one function; the storage data area may store data created from use of the laser altimeter cloud scattering error correction apparatus, and the like. Further, memory 92 may include high speed random access memory, and may also include non-transitory memory, such as at least one magnetic disk storage device, flash memory device, or other non-transitory solid state storage device. In some embodiments, memory 92 may optionally include memory located remotely from processor 91, and these remote memories may be connected to the laser altimeter cloud dispersion error correction device via a network. Input device 99 may receive user input of a calculation request (or other numeric or character information) and generate key signal inputs associated with the laser altimeter cloud dispersion error correction device. The output device 94 may include a display device such as a display screen for outputting the calculation result.
Example 4
The invention provides a computer-readable storage medium which stores computer instructions, wherein the computer-readable storage medium stores computer-executable instructions, and the computer-executable instructions can execute the laser altimeter cloud scattering error correction method in any method embodiment. The storage medium may be a magnetic Disk, an optical Disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a Flash Memory (Flash Memory), a Hard Disk (Hard Disk Drive, abbreviated as HDD), a Solid State Drive (SSD), or the like; the storage medium may also comprise a combination of memories of the kind described above.
It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (11)
1. A laser altimeter cloud scattering error correction method is characterized by comprising the following steps:
acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers of different altitudes;
calculating original height measurement data according to the echo waveform data;
calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power;
calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient;
calculating a weakening coefficient according to the backscattering coefficient and the extinction coefficient;
calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient;
calculating a height measurement deviation correction value according to the cloud optical thickness and a height measurement deviation model caused by atmospheric scattering;
and calculating corrected height measurement data according to the original height measurement data and the height measurement deviation correction value.
2. The method for correcting cloud scattering error of a laser altimeter according to claim 1, wherein the step of calculating backscattering coefficient and extinction coefficient at different altitudes according to the echo power comprises:
calculating the temperature, the air pressure and the relative humidity at different altitudes according to the echo power and a preset temperature function, a preset air pressure function and a preset relative humidity function at different altitudes;
calculating backscattering coefficients at different altitudes according to the temperature, the air pressure and the relative humidity at different altitudes;
and calculating extinction coefficients at different altitudes according to the backscattering coefficients.
3. The method for correcting the cloud scattering error of the laser altimeter according to claim 1, wherein calculating the cloud top height according to the backscattering coefficient comprises:
calculating top threshold values at different altitudes according to backscattering coefficients at different altitudes and a preset scattering constant;
and determining the altitude corresponding to the first backscattering coefficient larger than the top threshold as the cloud top height.
4. The laser altimeter cloud scattering error correction method of claim 3, wherein the top threshold is calculated by the following formula:
Tt＝(βm(z)+ψ)·F，
wherein, βmA backscatter coefficient indicating a current altitude, Ψ denotes a scattering constant, F ═ 0.70d0+ (i _ bin _ cnt/2)/180.0d0), i _ bin _ cnt denotes a node number of the current altitude, and d0 denotes that echo power received by the laser altimeter is converted into a quantized value between 0 and 255.
5. The method for correcting the cloud scattering error of the laser altimeter according to claim 3, wherein calculating the cloud base height according to the backscattering coefficient comprises:
calculating bottom thresholds at different altitudes according to backscattering coefficients at different altitudes, cloud top heights, node numbers of the cloud top heights and top thresholds corresponding to the cloud top heights;
and determining the altitude corresponding to the first backscattering coefficient larger than the bottom threshold as the cloud bottom height.
6. The method of claim 5, wherein the bottom threshold is calculated by the following formula:
Tb＝Tt-(i_bin_cnt-i_bin_top)·d_top_thr·0.0010，
wherein i _ bin _ top represents the node number of the cloud top height, and d _ top _ thr represents the top threshold corresponding to the cloud top height.
7. The method for correcting cloud scattering error of a laser altimeter according to claim 1, wherein the cloud optical thickness is calculated by the following formula:
wherein z istopDenotes the cloud ceiling height, zbottomRepresenting the height of the cloud base, Sα(z) represents the attenuation coefficient at altitude z.
8. The method for correcting the cloud scattering error of the laser altimeter according to claim 1, wherein the model of the altimetric deviation caused by atmospheric scattering is as follows:
Y＝a+b·Exp(c·τ)，
where τ represents the cloud optical thickness.
9. The utility model provides a laser altimeter cloud scattering error correcting unit which characterized in that includes:
the echo waveform data acquisition module is used for acquiring echo waveform data of the altimetry laser, wherein the echo waveform data comprises echo powers of different altitudes;
the original height measurement data calculation module is used for calculating original height measurement data according to the echo waveform data;
the backscattering coefficient calculation module is used for calculating backscattering coefficients and extinction coefficients at different altitudes according to the echo power;
the cloud detection module is used for calculating the height of the cloud top and the height of the cloud bottom according to the backscattering coefficient;
the attenuation coefficient calculation module is used for calculating an attenuation coefficient according to the backscattering coefficient and the extinction coefficient;
the cloud optical thickness calculating module is used for calculating the cloud optical thickness according to the cloud top height, the cloud bottom height and the weakening coefficient;
the height measurement deviation correction value calculation module is used for calculating a height measurement deviation correction value according to the cloud optical thickness and a height measurement deviation model caused by atmospheric scattering;
and the corrected height measurement data calculation module is used for calculating corrected height measurement data according to the original height measurement data and the height measurement deviation correction value.
10. A computer device, comprising:
at least one processor; and a memory communicatively coupled to the at least one processor; wherein the memory stores instructions executable by the at least one processor to perform the laser altimeter cloud dispersion error correction method of any one of claims 1-8.
11. A computer-readable storage medium storing computer instructions for causing a computer to perform the laser altimeter cloud scattering error correction method of any one of claims 1-8.
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