The software has been developed for thematic processing of data of Russian satellite systems. It is based on the algorithm of atmospheric correction developed by IAO SB RAS. The software allows retrieval of the reflection coefficients of the Earth's surface with the RTM atmospheric correction algorithm in the visible and near-IR range on the assumption of a uniform surface. The software includes converters for reading and unpacking input formats of satellite data and related metadata, an atmospheric correction module, and an auxiliary module for formation of the atmospheric model. The atmospheric correction includes procedures for statistical simulation of the Earth's surface illumination and for calculation of the spherical albedo of the atmosphere, intensity of radiation noninteracting with the surface, and intensity of radiation reflected by the surface.
system is assumed to be at the height hd from the surface. It is oriented in the direction ωd and observes some part of the surface. Let the spatial resolution of an optical receiver forming the image be constant within the observed zone. The parallel flux of solar radiation is incident on the atmospheric top in the direction ωsun. The radiation received by the satellite system consists of the sun haze Isun (solar radiation scattered in the atmosphere and noninteracting with the Earth’s surface), nonscattered radiation reflected from the observed part of the Earth’s surface I0, and the surface haze Isurf (scattered radiation reflected from the Earth’s surface).
With the known atmospheric parameters and intensities measured by the satellite system, the task is to retrieve the distribution of the reflection coefficient over the observed area of the Earth’s surface. 1. – – – –
However, in this version of the software, the problem of retrieval of the reflection coefficients is solved in the single approximation with the use of Eqs. (1) and (2) , =
⁄ 0 1+ 1 ⁄ 0 1 + , , − , , (1) (2) where rsurf,i is the Earth’s surface reflection coefficient; E0 is the Earth’s surface illumination with the ignored contribution of reflected radiation; γ1 is the spherical albedo of the atmosphere; Isum,i is the total intensity of received radiation; Isun,i is the intensity of the solar haze; Ti is the direct transmission coefficient from an observed pixel to the receiving system; Idif,i is the intensity of the surface haze at the unit luminosity of the Earth’s surface. 3
Model data, RSE data, prognostic data, radio balloon data, AERONET network data, and others can be used as information about the optical and meteorological state of the atmosphere at the time of satellite measurements. Among the mentioned types, only RSE data can be obtained in real time and provide the relatively high spatial resolution comparable with the spatial resolution of satellite radiometric channels.
As a result of the studies accomplished in IAO SB RAS, a technique for using the data on the state of the
atmosphere from MODIS spectroradiometer measurements in the atmospheric correction of satellite IR images was
proposed and justified [
Within the scope of the developed software, the data on optical properties of the atmosphere are saved in the optical model of the atmosphere, which is generated by the specially developed code. The model of the atmosphere is formed for data of every channel of the satellite device and includes the following parameters: solar constant, profiles of aerosol and molecular extinction and scattering coefficients, and scattering phase function for 32 atmospheric layers in the height range from 0 to 100 km. In addition, the model includes instrumental characteristics of the devices.
The MODIS spectroradiometer measurement data are used as a source of information about atmospheric parameters. Data of ground-based measurements can be invoked as an alternative. Basic characteristics for construction of the optical model are the central radiation wavelength λ, width Δλ and the instrument function of a measurement instrumentation channel, aerosol optical thickness of the atmosphere at λ = 0.47, 0.55, and 0.66 µm, total ozone content, surface pressure, total water vapor column, and vertical temperature profile.
For formation of the models of optical properties of the atmosphere at the observation time (or close time), the software uses the data on solar constants, absorption spectra of O2, O3, and H2O, LOWTRAN-7 aerosol models, total water vapor column, total ozone content, and data on molecular scattering coefficients of the air under normal conditions. 4
The atmospheric correction software can perform the following functions: 1) decoding the data of satellite measurements and related metadata, preparing the data for calculations, saving the calculated results in the standard format; 2) forming the optical model of the atmosphere; 3) calculating radiation fluxes forming the radiation received by the satellite device; 4) performing the atmospheric correction.
The software functions are executed by different modules.
The module of data preparation includes a converter for reading and saving the initial data and calculated results
in the GeoTIFF format [
The module for calculation of atmospheric correction additions is a set of Fortran programs. Calculations are
performed by the Monte Carlo technique with the algorithms taking into account the atmospheric sphericity [
The order of data processing and call of converters and computation modules is set by the Python control module. Our software operates in the Linux operation system. It was developed and tested in the openSUSE leap 42.3 environment. The software operation is shown schematically in Figure 2.
Free software was used as development tools.
The software package under consideration serves for retrieval of the reflection coefficients (albedo) of the Earth’s surface from satellite measurements of light fluxes by Russian Sangur and GSA devices of the Resurs-P satellite and KMSS of the Meteor-M satellite. In the first version of this software, a separate control module was developed for each device because of insufficient standardization of satellite data and metadata formats.
For the further development of the software for thematic processing of data of Russian satellite devices, we plan 1. To include additional calculation modules providing for calculation of atmospheric correction additions; 2. To increase the computation speed by using parallel programming technologies; 3. To include the generator of optical models of the atmosphere into the software. To use network sources of data necessary for formation of optical models of the atmosphere as a component of the software; 4. To develop the user interface. To complement it with imaging tools and tools for analysis of satellite images; 5. To extend the list of satellite devices, whose data can be processed with the proposed software.