CN112903631B - Inland river surface water body reflection spectrum navigation observation method - Google Patents
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Abstract
The invention discloses a inland river channel surface water body reflection spectrum navigation observation method, which comprises the following steps: arranging an actual measurement instrument for continuously observing the reflection spectrum of the surface water body of the inland river channel, and adjusting the angle of the actual measurement instrument according to the requirement of vertical observation to realize synchronous observation of the gray plate, the skylight and the water surface reflection light; using observed values of the gray plate, the sky light and the water surface reflected light measured by the actual measurement instrument to calculate remote sensing reflectivity, and identifying and eliminating abnormal values of the remote sensing reflectivity obtained by calculation; and performing time-space matching on the obtained remote sensing reflectivity of the surface water body of the inland river channel to obtain the remote sensing reflectivity of the surface water body of the inland river channel which is continuous in time and space. The invention realizes continuous spectrum observation, improves the space-time continuity and can accurately grasp the spectrum change condition of a large-scale water body.
Description
Technical Field
The invention relates to the technical field of water spectrum measurement, in particular to a method for observing reflection spectrum navigation of an inland river surface water body.
Background
The measurement of the optical characteristics of the water body is an indispensable basic research process for the remote sensing inversion of the water color. The optical characteristics of the water body comprise inherent optical characteristics and apparent optical characteristics, wherein the inherent optical characteristics are only determined by the physical characteristics of the water body, and are not changed along with the change of an external incident light field, such as absorption coefficient, attenuation coefficient, scattering coefficient and the like; the apparent optical characteristics are water optical parameters which change along with the change of an incident light field, such as the brightness of the water-leaving radiation, the irradiance of the uplink, the remote sensing reflectivity and the like.
The optical characteristic of inland water body is studied by taking apparent optical characteristic measurement as an initial data source, and the basic parameter is the brightness of the radiation of water. The measurement method of the brightness of the leaving water comprises a section measurement method and a measurement method above the water surface. The profile measurement method is a method for longitudinally measuring the optical characteristics of underwater water bodies at different depths and extrapolating to obtain optical signals of the water surface so as to obtain remote sensing physical quantities such as the brightness of the leaving water, the normalized brightness of the leaving water, the remote sensing reflectivity and the like, and the method is widely applied to ocean-type water bodies and is inapplicable to inland-type water body areas. The above-water measurement method is a main method for measuring two kinds of water bodies recommended by NASA SeaWiFS measurement standards, is a water body measurement method widely used by scholars at home and abroad at present, and takes precedence in spectral characteristic investigation means of inland water bodies such as near-shore water bodies, lakes, river channels and the like in China by selecting proper observation geometry above the water surface, observing targets such as skylight on the water surface, incident irradiance on the water surface and the like, and obtaining remote sensing physical quantities the same as the profile measurement method.
The water body spectral characteristics are external characterization of water body optical components, and the remote sensing reflectivity of the water body can be calculated by utilizing the actually measured water-leaving radiance and sky light radiance of the water body, so that the spectral characteristics of the water body are analyzed. At present, the optical measurement of the water body adopts an oblique observation method, and mainly adopts the observation angle (40 degrees and 135 degrees) recommended to be used in the international water color SIMBIOS program, namely, the included angle between the observation plane of the spectrometer and the incident plane of the sun is 135 degrees (back to the sun), the included angle between the instrument and the normal direction of the sea surface is 40 degrees, and the observation geometry is considered to reduce the influence of the flare of the hull and the water surface to the greatest extent.
As the inclination observation needs to adjust the observation angle according to the relative factors such as the ship body position, the sun azimuth and the like, especially when aiming at the spectrum observation of the river water body, the conditions such as the river trend, the shoreline shielding and the like need to be considered. Therefore, at the present stage, a plurality of sites can be set for observing discrete sample points, and continuous spectrum observation is difficult to realize. Although the observation method of the discrete sample points can accurately measure and analyze the optical characteristics of the local water body, the time and the labor are wasted and the number of the observation sample points is limited. Therefore, the observation method of the discrete sample points has the defects of insufficient representativeness of actual measurement data, low space-time continuity, difficulty in grasping the spectrum change condition of a large-scale water body and the like.
The invention with publication number CN 109084894B discloses a sailing type water spectrum observation system and an observation method, wherein the system comprises a bracket, a triaxial self-stabilizing platform, an observation instrument and a deck control unit; the observation instrument comprises a radiance radiometer, a irradiance radiometer, an electronic compass, an attitude sensor, a GPS antenna and a camera; the bracket is used for fixedly mounting the whole observation system on the outer side of the navigation observation ship body, and one end of the bracket, which is farthest from the ship, is provided with a triaxial self-stabilizing platform, a high point is provided with an irradiance radiometer, and other arbitrary positions are provided with GPS antennas; the pitching rotating shaft of the triaxial self-stabilizing platform is fixedly connected with the instrument frame; at least an electronic compass, an attitude sensor, a radiance radiometer and a camera are arranged on the instrument frame; the deck control unit is used for supplying power to the observation instrument, communicating with the observation instrument through built-in software and completing the processing of observation data through the built-in software. The invention is mainly designed for a sailing type water spectrum observation system of the ocean water, so the system and the corresponding observation method mainly solve the problem that observation equipment carried by an experimental ship is easy to vibrate and shake along with waves in sailing type observation.
The invention discloses a lake water body spectral reflectance inspection method and device, wherein the publication number is CN 111879709A, and the method comprises the following steps: screening the actually measured water body spectral reflectance by using a preset water body spectral reflectance prediction model; the water body spectral reflectance prediction model is obtained after training based on water body parameter sample data, environment parameter sample data and corresponding water body sample spectral reflectance; the measured spectral reflectance of the water body is obtained by sampling and detecting the water body to be measured through measuring equipment; and checking and correcting the satellite inversion algorithm according to the screened actual measured water body spectral reflectivity, and acquiring the water body spectral reflectivity to be detected by using the corrected satellite inversion algorithm. According to the invention, the water body spectral reflectance obtained by satellite inversion is verified and corrected through the screened actual measured water body spectral reflectance, and the defect of low reliability of the existing water body spectral reflectance obtained by satellites is overcome.
Disclosure of Invention
According to the invention, by acquiring a large amount of water body reflection spectrum data which are continuous in time and space, the rapid continuous inland river surface water body reflection spectrum navigation observation is realized.
An inland river surface water reflection spectrum navigation observation method comprises the following steps:
1. arranging an actual measurement instrument for continuously observing the reflection spectrum of the surface water body of the inland river channel, and adjusting the angle of the actual measurement instrument according to the requirement of vertical observation to realize synchronous observation of the gray plate, the skylight and the water surface reflection light;
2. using observed values of the gray plate, the sky light and the water surface reflected light measured by the actual measurement instrument to calculate remote sensing reflectivity, and identifying and eliminating abnormal values of the remote sensing reflectivity obtained by calculation;
3. and (3) performing time-space matching on the remote sensing reflectivity of the inland river channel surface water body obtained in the step (2) to obtain the remote sensing reflectivity of the inland river channel surface water body which is continuous in time and space.
Preferably, the actual measurement instrument adopts a spectrometer.
Further preferably, before the positioning, the gray plate is calibrated for the spectrometer to obtain the radiance value of the spectrometer, and the calibration coefficients of the spectrometer for observing the sky light and the water surface reflected light are calculated respectively by taking the calibration result of the spectrometer of the in-situ actually measured gray plate as the reference. Because of the differences of the types of the spectrometers, the responses of the photosensitive elements, the external optical fibers and the like, the measured data have consistency errors, and the calibration coefficients can reduce errors caused by equipment factors such as the spectrometers, the external optical fibers and the like.
Preferably, the measured environment during the fast continuous navigation observation is controlled, comprising the following steps: the method comprises the steps of selecting a small water surface wave for observation, wherein the hull of a test ship is prevented from shaking; the test ship runs at a constant speed in the middle of the river channel, so that the influence of the shoreline shielding object and the shadow on the observation is avoided as much as possible.
Further preferably, the step of positioning the spectrometer comprises:
1.1 an optical fiber probe of an external optical fiber of the spectrometer is fixed on a bracket of the gray plate and is used for observing the gray plate;
1.2 two spectrometers are respectively connected with corresponding external optical fibers, and then are fixed on a probe bracket according to the requirement of a measurement method above the water surface, and are respectively used for observing sky light and water surface reflected light, the fixed positions of the spectrometers are required to meet the conditions of a certain distance from the water surface, no shielding object, sufficient light and the like, and meanwhile, the observation time is required to avoid a midday period with a smaller zenith angle of the sun so as to reduce the influence of solar shining.
The step 1 is to install an actual measurement instrument for rapidly observing the reflection spectrum of the surface water body of the inland river channel according to the particularity of the inland river channel on the basis of a measurement method on the water surface of the second-class water body, so that continuous navigation observation of the reflection spectrum of the water body is realized.
And step 1, adjusting the optical fiber probe of the spectrometer to be parallel to the normal line of the water body surface according to the requirement of vertical observation, namely, the condition that the zenith angle of observation is 0 degree (observation of water surface reflected light) or 180 degrees (observation of sky light) respectively.
The angle of the spectrometer is set by adopting a vertical observation method, and the optical fiber probes of the spectrometer are respectively arranged to be vertical to the gray plate, the sky and the water surface for synchronous observation. Although the (40 degrees, 135 degrees) is the observation geometry of the two types of water bodies recommended to be used at present, the inclined observation needs to adjust the observation angle at any time according to the conditions of the river course, the ship body position, the shoreline shielding, the sun azimuth and the like, so that the method is not suitable for the rapid continuous observation of the inland river water bodies. After comprehensively considering the particularity of inland water bodies, particularly river water bodies, the angle of the observation geometry is adjusted to be (0 degrees, 180 degrees) for the purpose of quick observation.
Preferably, the step of calculating the remote sensing reflectivity in the step 2, and identifying and eliminating the abnormal value of the calculated remote sensing reflectivity includes:
2.1 exporting and format conversion of spectrometer data, exporting actual measurement data of the spectrometer by using matching software, exporting the data into an ASD format, checking the exported data by using ViewSpecPro, and converting the ASD format into a TXT format required by a continuous observation-oriented spectral reflection data processing system;
2.2 removing abnormal values of the actually measured radiance of the water body, outputting the data obtained in the step 2.1 to a spectral reflection data processing system to read each piece of data of the TXT file, selecting characteristic wavelengths to check and identify obvious abnormal values, and finally removing the abnormal values, wherein the abnormal values are mainly caused by shielding of bridges on a river channel during navigation observation.
2.3, calculating the remote sensing reflectivity Rrs of the water body:
in the method, lw, lsky, es is the measured value when the spectrometer faces to the water body, the sky and the standard gray plate, and ρ p For the standard gray plate reflectivity subjected to strict calibration, the reflectivity of rho gas-water interface to skylight, and alpha and beta are calibration coefficients of skylight and water surface reflected light respectively.
2.4 removing and smoothing abnormal values of remote sensing reflectivity: and 2.3, after the remote sensing reflectivity of the inland river surface water body is obtained, selecting characteristic wavelength again to check and identify the abnormal value of the calculated remote sensing reflectivity, and then carrying out mean value filtering on the remote sensing reflectivity of the inland river surface water body after the abnormal value is removed to realize data smoothing and obtain the corrected remote sensing reflectivity.
In the step 2.4, a threshold value is set firstly, and then the difference value of the front data and the rear data of the set threshold value is compared with the threshold value, so that abnormal remote sensing reflectivity is eliminated.
And 2, calculating remote sensing reflectivity of the inland river surface water body based on measured data, and identifying and eliminating abnormal values, wherein the aim of rapid and continuous observation is achieved. The identification and elimination of all data outliers is implemented in a continuously observation oriented spectral reflectance data processing system.
Preferably, the step 3 is a space-time synchronous matching between the remote sensing reflectivity data obtained in the step 2 and satellite positioning data, and the specific steps include the following steps:
3.1 time synchronization of remote sensing reflectivity of the surface water body of the inland river channel, interpolation processing is carried out on the whole second moment lacking spectrum data recording by adopting the average value of two spectrum data before and after the whole second moment, and substitution processing is carried out on the whole second moment with a plurality of spectrum data recorded by the spectrum data, so that a spectrum data result at the whole second moment is obtained, and continuous observation in time is achieved.
3.2, spatially synchronous positioning of the surface water body remote sensing reflectivity of the inland river channel, namely interpolating synchronous whole second longitude and latitude data according to the data of the whole second after processing in the step 3.1 by utilizing satellite positioning data of continuous observation, so that time-space matching of the longitude and latitude data and the surface water body remote sensing reflectivity data of the inland river channel is realized, and the surface water body remote sensing reflectivity of the inland river channel which is continuous in time and space is obtained.
Compared with the prior art, the invention has the advantages that:
1. by adopting vertical observation, the measurement angle does not need to be adjusted, the measured consistency can be ensured, the stability is better, most uncertain factors can be eliminated by calculating the spectral reflectance of vertical measurement, and the method is completely in line with the construction of inversion models and the study of the spectral characteristics of water quality.
2. Because the spectrum acquisition also refers to factors such as solar altitude, acquisition time and the like, the spectrum characteristics are further improved, time and longitude and latitude space matching is performed, and the space-time continuity of the water remote sensing reflectivity data is improved. Meanwhile, as the zenith angle of observation of most satellite sensors is close to 0, namely near vertical observation, the invention not only can obtain a large number of continuous reflection spectrum data of the surface water body of the inland river channel, but also can be applied as measured data which is more similar to the observation geometry of satellite images.
Drawings
FIG. 1 is a schematic diagram of a spectrometer cross-calibration geometry according to an embodiment of the present invention.
FIG. 2 is a graph of the calibration coefficients of a spectrometer according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of the actual measurement geometry of the spectrometer according to the embodiment of the invention.
FIG. 4 shows the characteristic wavelength remote sensing reflectivity obtained after data rationality inspection and correction in accordance with an embodiment of the present invention.
FIG. 5 shows the time-continuous remote sensing reflectivity obtained after data plausibility inspection and correction according to an embodiment of the present invention.
FIG. 6 shows the spatially-continuous remote sensing reflectivity obtained after the spatial-temporal matching according to the embodiment of the present invention.
Detailed Description
An inland river surface water reflection spectrum navigation observation method comprises the following steps:
(1) Arranging an actual measurement instrument for continuously observing the reflection spectrum of the surface water body of the inland river channel, and adjusting the angle of the actual measurement instrument according to the requirement of vertical observation to realize synchronous observation of the gray plate, the skylight and the water surface reflection light;
(2) Using observed values of the gray plate, the sky light and the water surface reflected light measured by the actual measurement instrument to calculate remote sensing reflectivity, and identifying and eliminating abnormal values of the remote sensing reflectivity obtained by calculation;
(3) And (3) performing time-space matching on the remote sensing reflectivity of the inland river channel surface water body obtained in the step (2) to obtain the remote sensing reflectivity of the inland river channel surface water body which is continuous in time and space.
The river course shown in fig. 6 is selected to carry out the fast continuous inland river course surface water reflection spectrum navigation observation, and the specific steps are as follows:
s1.1 is shown in FIG. 1, gray plate calibration is carried out on a spectrometer to obtain a corresponding radiance value, and calibration coefficients of sky light and water surface reflected light are calculated and obtained, as shown in FIG. 2. Because of the differences of the types of the spectrometers, the responses of the photosensitive elements, the external optical fibers and the like, the measured data have consistency errors, and the calibration coefficients can reduce errors caused by equipment factors such as the spectrometers, the external optical fibers and the like.
S1.2 as shown in FIG. 3, an optical fiber probe of an external optical fiber of a spectrometer is fixed on a bracket of the gray plate and used for observing the gray plate.
S1.3 as shown in FIG. 3, two spectrometers are respectively connected with corresponding external optical fibers and then fixed on a probe bracket according to the requirement of a measurement method above the water surface, and the two spectrometers are respectively used for observing sky light and water surface reflected light, wherein the fixed positions of the spectrometers are required to meet the conditions of a certain distance from the water surface, no shielding object, sufficient light and the like, and meanwhile, the observation time is required to avoid an inter-noon period with a smaller zenith angle of the sun so as to reduce the influence of solar shining.
S1.4, setting the angle of a spectrometer by adopting a vertical observation method, wherein optical fiber probes of the spectrometer are respectively arranged to be vertical to an ash plate, the sky and the water surface for synchronous observation.
S1.5, observing when the wind and waves on the water surface are small, wherein the hull of the test ship is prevented from shaking; the test ship runs at a constant speed in the middle of the river channel, so that the influence of the shoreline shielding object and the shadow on the observation is avoided as much as possible.
S2.1, data export and format conversion of the spectrometer, wherein measured data of the spectrometer are exported by using matching software of the spectrometer, the exported data are in an ASD format, the exported data are checked by using ViewSpecPro, and the ASD format is converted into a TXT format required by a continuous observation-oriented spectral reflection data processing system.
S2.2, removing abnormal values of the actually measured radiance of the water body, wherein the spectral reflection data processing system reads each piece of data of the TXT file, then selects characteristic wavelengths to view and identify obvious abnormal values, and finally removes the abnormal values, as shown in fig. 4.
S2.3, calculating the remote sensing reflectivity Rrs of the water body:
lw, lsky, es is the measured value of the spectrometer facing the water, sky and standard gray plate，ρ p For the standard gray plate reflectivity subjected to strict calibration, the reflectivity of rho gas-water interface to skylight, and alpha and beta are correction coefficients of skylight and water surface reflected light respectively.
S2.4, removing and smoothing abnormal values of remote sensing reflectivity: after obtaining the remote sensing reflectivity of the inland river surface water body through S3.3, selecting characteristic wavelength again to check and identify the abnormal value of the calculated remote sensing reflectivity, removing the abnormal remote sensing reflectivity by adopting a method of firstly setting a threshold value and then comparing the difference value of the front data and the rear data with the threshold value, and then carrying out mean value filtering on the remote sensing reflectivity of the inland river surface water body from which the abnormal value is removed to realize data smoothing, so as to obtain the corrected remote sensing reflectivity, as shown in figure 5.
S3.1, time synchronization of remote sensing reflectivity of the surface water body of the inland river channel, interpolation processing is carried out on the whole second moment lacking spectrum data recording by adopting the average value of two spectrum data before and after the whole second moment, and substitution processing is carried out on the whole second moment with a plurality of spectrum data recorded by the spectrum data, so that a spectrum data result at the whole second moment is obtained, and continuous observation in time is achieved. Since the data is set to be one piece of data in 1 second when the spectrometer observes, but since the spectrometer records the phenomena such as data delay, the spectrum data is not recorded in whole seconds, and therefore time matching processing is required.
S3.2, spatially synchronous positioning of the surface water body remote sensing reflectivity of the inland river channel is achieved by interpolating synchronous whole-second longitude and latitude data according to the whole-second time data processed in the step 3.1 by using satellite positioning data of continuous observation, so that time-space matching of the longitude and latitude data and the surface water body remote sensing reflectivity data of the inland river channel is achieved, and the surface water body remote sensing reflectivity of the inland river channel is continuous in time and space, as shown in fig. 6.
Claims (6)
1. The inland river channel surface water reflection spectrum navigation observation method is characterized by comprising the following steps of:
(1) An actual measurement instrument for continuously observing the reflection spectrum of the surface water body of the inland river channel is arranged, the actual measurement instrument adopts a spectrometer, the angle of the spectrometer is adjusted according to the requirement of vertical observation, and an optical fiber probe of the spectrometer is respectively arranged to be vertical to an ash plate, the sky and the water surface, so that synchronous observation of the ash plate, the sky light and the water surface reflection light is realized;
(2) The method comprises the following steps of calculating remote sensing reflectivity by using observed values of gray plate, sky light and water surface reflected light measured by a spectrometer, and identifying and eliminating the abnormal value of the calculated remote sensing reflectivity, wherein the steps are as follows:
(2.1) exporting spectrometer data, and converting a data format exported by the spectrometer into a format of a spectral reflection data processing system facing continuous observation;
(2.2) removing abnormal values of the actually measured radiance of the water body, outputting the data obtained in the step (2.1) to a spectral reflectance data processing system, selecting characteristic wavelengths to view and identify the abnormal values, and finally removing the abnormal values;
(2.3) calculating the remote sensing reflectivity R of the water body rs ，
Wherein L is w 、L sky 、E s Measured values when the spectrometer faces to water, sky and standard gray plate, ρ p The standard gray plate reflectivity is ρ, the reflectivity of the air-water interface to the skylight, and alpha and beta are the calibration coefficients of the skylight and the water surface reflected light respectively;
(2.4) removing and smoothing abnormal values of the remote sensing reflectivity, after the remote sensing reflectivity of the surface water body of the inland river channel is obtained in the step (2.3), selecting characteristic wavelengths again to check and identify the calculated abnormal values of the remote sensing reflectivity, and then carrying out mean value filtering on the remote sensing reflectivity of the surface water body of the inland river channel after removing the abnormal values to realize data smoothing and obtain corrected remote sensing reflectivity;
(3) Performing time-space matching on the remote sensing reflectivity of the inland river channel surface water body obtained in the step (2) to obtain the remote sensing reflectivity of the inland river channel surface water body which is continuous in time and space, wherein the method comprises the following specific steps:
(3.1) time synchronization of remote sensing reflectivity of the surface water body of the inland river channel, carrying out interpolation processing on the whole second moment lacking the spectrum data record by adopting the average value of two spectrum data before and after the whole second moment, and carrying out substitution processing on the whole second moment with a plurality of spectrum data in the moment by using the average value of the plurality of spectrum data in the moment to obtain a spectrum data result of the whole second moment so as to achieve continuous observation in time;
and (3.2) spatially synchronous positioning of the remote sensing reflectivity of the surface water body of the inland river channel, and interpolating synchronous whole-second longitude and latitude data according to the data of the whole second time processed in the step (3.1) by utilizing satellite positioning data of continuous observation, so as to realize time-space matching of the longitude and latitude data and the remote sensing reflectivity data of the surface water body of the inland river channel, and obtain the remote sensing reflectivity of the surface water body of the inland river channel which is continuous in time and space.
2. The method for observing the reflection spectrum of the surface water body of the inland river channel according to claim 1, wherein the gray plate is calibrated for the spectrometer before the arrangement to obtain the radiance value of the spectrometer, and the calibration coefficients of the spectrometer for observing the skylight and the water surface reflection light are respectively calculated by taking the calibration result of the spectrometer of the pre-determined in-situ actually measured gray plate as a reference.
3. The method of claim 1, wherein the step of positioning the spectrometer comprises:
(1.1) an optical fiber probe of an external optical fiber of the spectrometer is fixed on a bracket of the gray plate and is used for observing the gray plate;
and (1.2) the two spectrometers are respectively connected with corresponding external optical fibers and then fixed on the probe support according to the requirement of a measurement method above the water surface, and are respectively used for observing sky light and water surface reflected light.
4. The inland river surface water reflection spectrum navigation observation method of claim 1, wherein the fiber probe of the spectrometer is parallel to the water surface normal.
5. The inland river surface water body reflection spectrum navigation observation method of claim 1, wherein in the step (2.4), a threshold value is set first, and then the abnormal remote sensing reflectivity is removed according to the difference value between the front data and the rear data of the set threshold value and the threshold value.
6. The inland river channel surface water reflection spectrum navigation observation method of claim 1, wherein the actual measurement environment during the rapid continuous navigation observation is controlled, comprising the following steps: the ship body of the test ship is prevented from shaking, and the influence of the shoreline shielding object and the shadow on observation is prevented.
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