A Method for Retrieving Land Surface Temperature from FY3 VIRR Data

Abstract

The present invention discloses a land surface temperature inversion algorithm applicable to FY3 VIRR data, which calculates the brightness temperature values T4 and T5 of the thermal infrared channels, calculates the land surface emissivity ε4 and ε5 through the data of the visible and near-infrared channels, and substitutes these two parameters into the land surface temperature inversion algorithm model to invert the land surface temperature. This method is completely based on the FY3 VIRR data itself and does not require external data, overcoming the difficulty that the land surface temperature inversion algorithm needs to rely on external data to invert parameters. At the same time, the present invention presents a land surface temperature inversion algorithm applicable to FY3 VIRR data, improving the inversion accuracy of its land surface temperature. Through a simple and clear logical relationship, the invention enables non-professionals to clearly understand the algorithm and carry out practical operations and applications, providing strong theoretical and technical support for it.

Description

Technical Field

[0001] The present invention relates to a method for retrieving land surface temperature using the Visible and Infrared Radiometer (VIRR) sensor carried by Fengyun-3 satellite, which can be widely used in agricultural monitoring, environmental monitoring, land surface drought monitoring, forest fire monitoring, etc. Background Art

[0002] Land Surface Temperature (LST) is defined as the skin temperature of the land surface. Due to the spatio-temporal differentiation characteristics of the land surface temperature, the accuracy and spatial expression ability of spatial interpolation using meteorological station data have great uncertainties. The traditional ground-based fixed-point temperature measurement has discreteness in distribution, and the measurement coverage is quite limited, making it difficult to meet various application requirements. Satellite remote sensing technology can, to a certain extent, make up for these deficiencies. Retrieving the land surface temperature using remote sensing methods based on thermal infrared data can obtain the land surface temperature over a large range, which has great value for the research on the interaction between the land-atmosphere system at medium and large scales, and can be widely used in agricultural monitoring, environmental monitoring, land surface drought monitoring, forest fire monitoring, etc.

[0003] FY3 is the second-generation polar-orbiting meteorological satellite in China, and VIRR is the sensor carried by it. Both the 4th and 5th channels are thermal infrared channels, which can be used to extract land surface characteristic parameters. As a new and important satellite data source, it has great application prospects in retrieving the land surface temperature.

[0004] Currently, most of the existing land surface temperature retrieval algorithms are proposed for foreign sensors, such as MODIS, TM, etc. Therefore, the purpose of the present invention is to use VIRR data as the main data source, combine the spectral characteristics of the thermal infrared channels of the sensor, obtain the land surface emissivity based on the land surface cover type, and study a high-precision land surface temperature retrieval algorithm suitable for FY3 VIRR, so as to provide reliable services for relevant fields such as national meteorology, agriculture, environment, and disaster monitoring. Summary of the Invention

[0005] The purpose of the present invention is to provide a land surface temperature retrieval algorithm suitable for FY3 VIRR data, aiming to improve the accuracy of the land surface temperature retrieval algorithm for FY3 VIRR data. By recalculating the parameters in the Becker and Li split-window algorithm and combining the spectral response function of FY3 VIRR, the accuracy of the land surface temperature retrieval algorithm is improved, which is very beneficial for the understanding and application of non-professionals.

[0006] The present invention is implemented as follows. The FY3 VIRR land surface temperature retrieval method includes the following steps:

[0007] Step 1: Calculation of the brightness temperature of the FY3 VIRR thermal infrared channel, including four sub-steps:

[0008] (1) On-orbit linear calibration. The formula is as follows:

[0009] N LIN = S c × C E + O f

[0010] In the formula, N LIN is the radiance value calculated using the on-orbit calibration coefficient (unit: mW / m 2 ·cm -1 ·sr), S c is the gain, O f is the intercept, and C E is the digital value recorded by the FY3 VIRR sensor.

[0011] S E and O f are provided by the attribute sets Emissive_Radiance_Scales and Emissive_Radiance_Offces of the FY3 VIRR data;

[0012] (2) Nonlinear correction of radiance. The formula is as follows:

[0013]

[0014] In the formula, N is the radiance value after nonlinear correction (unit: mW / m 2 ·cm -1 ·sr), and b 0 , b 1 , b 2 are the correction coefficients. The correction coefficients are provided by the attribute set Prelaunch_Nonlinear_Coefficients of the FY3 VIRR data;

[0015] (3) Calculate the effective blackbody temperature. The formula used is as follows:

[0016]

[0017] In the formula is the effective blackbody temperature (K), c 1 = 1.1910427 × 10 -5 mW / (m 2 ·sr·cm -4 ), c 2 = 1.4387752 cm·K, and v c is the center wavenumber of the infrared channel obtained by ground calibration;

[0018] The central wave number of the infrared channel is provided by the attribute set Emissive_Centroid_Wave_Number of FY3 VIRR data;

[0019] (4) Calculate the blackbody temperature, that is, the brightness temperature of the thermal infrared channel. The formula is as follows:

[0020]

[0021] In the formula, T BB is the blackbody temperature (K), and A and B are constants;

[0022] A and B are provided by the attribute set Emissive BT Coefficents of FY3 VIRR data;

[0023] Step 2: Calculate the land surface emissivity. The specific steps are as follows:

[0024] (1) Calculate NDVI. The formula is as follows:

[0025]

[0026] In the formula, ρ 1 and ρ 2 are the reflectance values of the first and second bands in the visible and near-infrared spectral regions of FY3 VIRR, respectively.

[0027] (2) Calculate FVC. The formula is as follows:

[0028]

[0029] In the formula, P v is the vegetation coverage, NDVI v is the NDVI value of the area completely covered by vegetation, that is, the NDVI value of pure vegetation pixels, and NDVI s is the NDVI value of the area completely covered by bare soil or without vegetation.

[0030] (3) Calculate the land surface emissivity. The formula is as follows:

[0031] ε i = P v R v ε iv +(1 - P v )R s ε is + d ε

[0032] In the formula, ε i represents the land surface emissivity of the i-th band of the image, ε iv and ε isrepresent the surface emissivity of vegetation and bare soil in the i-th band, respectively. According to the surface emissivity database of the University of California, the emissivities of vegetation and bare soil in channels 4 and 5 of the FY-3 Visible and Infrared Scanner Radiometer are taken as ε 4v = 0.98672, ε 5v = 0.98990, ε 4s = 0.96767, ε 5s = 0.97790; P v represents the vegetation coverage of the pixel, d ε is the thermal radiation interaction correction, which is generated by the thermal radiation interaction between vegetation and bare soil, R v and R s are the radiation ratios of vegetation and bare soil, respectively, and the calculation formulas are as follows:

[0033] R v = 0.92762 + 0.07033P v

[0034] R s = 0.99782 + 0.08362P v

[0035] Step 3: Substitute the brightness temperature of the thermal infrared channel and the surface emissivity into the surface temperature inversion algorithm model:

[0036] T s = -0.143 + P(T 4 + T 5 ) / 2 + M(T 4 - T 5 ) / 2

[0037] P = 1 + 0.122(1 - ε) / ε - 0.061Δε / ε 2

[0038] M = 5.393 + 7.702(1 - ε) / ε - 3.876Δε / ε 2

[0039] ε = (ε 4 + ε 5 ) / 2

[0040] Δε = (ε 4 - ε 5 ) / 2

[0041] where, T 4 is the brightness temperature of the 4th channel of FY3 VIRR (K), T 5 is the brightness temperature of the 5th channel (K), ε 4 is the surface emissivity of the 4th channel, ε 5 is the surface emissivity of the 5th channel; Description of the Drawings

[0042] Figure 1 : Flow chart for retrieving land surface temperature from FY3 VIRR data Detailed Implementation Manner

[0043] As Figure 1 (Flow chart for retrieving land surface temperature from FY3 VIRR), the specific implementation steps of the present invention are as follows:

[0044] A method for retrieving land surface temperature from FY3 VIRR data, the specific implementation steps are as follows:

[0045] Step 1: Calculation of the brightness temperature of the FY3 VIRR thermal infrared channel, the specific implementation steps are as follows: Referring to Step 1, it is divided into four steps:

[0046] (1) Substitute the image DN value into the formula to calculate the radiance value N of one scene of the image LIN ;

[0047] (2) According to the radiance value N obtained in (1) LIN , substitute it into the radiance non-linear correction formula to calculate N;

[0048] (3) Substitute the non-linear correction result N in (2) into the formula for calculating the effective blackbody temperature to calculate

[0049] (4) According to the effective blackbody temperature result in (3) Substitute it into the brightness temperature formula to calculate T 4 、T 5 ;

[0050] Step 2: Calculate the land surface emissivity, the specific implementation steps are as follows:

[0051] First, calculate the NDVI and FVC of one scene of the image according to the formula, and then use the formula. Taking FVC as a known parameter, calculate Rv and Rs. Substitute the calculated Rv, Rs, and related known parameters into the calculation formula to obtain the land surface emissivity of one scene of the image;

[0052] Step 3: Substitute the brightness temperature of the thermal infrared channel and the land surface emissivity into the land surface temperature inversion algorithm model, the specific implementation steps are as follows:

[0053] According to Step 1 and Step 2, calculate the brightness temperatures T4 and T5 of the thermal infrared channels of FY3 VIRR and the land surface emissivities ε4 and ε5 respectively. Substitute the land surface emissivity parameter into the formula to calculate the unknown parameters P and M. Further substitute P, M, T4, and T5 into the calculation of the land surface temperature inversion parameters to obtain the land surface temperature inversion result of one scene of the image;

[0054] The parts not described in the present invention belong to well-known technologies.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for retrieving land surface temperature from FY3 VIRR data, characterized in that, the land surface temperature retrieval algorithm includes the following steps: Step 1: Calculate the brightness temperatures T 4 and T 5 of the thermal infrared channels using the data from the 4th and 5th channels of FY3 VIRR; 4 and T 5 ; Step 2: Calculate the land surface emissivity ε using FY3 VIRR visible and near-infrared data 4 and ε 5 ; Step 3: Substitute the parameters calculated in the above two steps into the land surface temperature retrieval algorithm model to obtain the land surface temperature retrieval result; The process of calculating the brightness temperature of the thermal infrared channel in Step 1 is as follows: (1) On-orbit linear calibration, the formula is as follows: N LIN = S c × C E + O f where N LIN is the radiance value calculated using the on-orbit calibration coefficient, with the unit of mW / m 2 ·cm -1 ·sr, S c is the gain, O f is the intercept, C E is the digital value recorded by the FY3 VIRR sensor; (2) Nonlinear correction of radiance, the formula is as follows: where N is the radiance value after non-linear correction, with the unit of mW / m 2 ·cm -1 ·sr, b 0 、b 1 、b 2 are correction coefficients; (3) Calculate the effective blackbody temperature, and the used Plank formula is as follows: where is the effective blackbody temperature, c 1 = 1.1910427×10 -5 mW / (m 2 ·sr·cm -4 ), c 2 = 1.4387752 cm·K, v c is the central wavenumber of the infrared channel obtained by ground calibration; (4) Calculate the blackbody temperature, that is, the brightness temperature of the thermal infrared channel, the formula is as follows: where T BB is the blackbody temperature, and A and B are constants; The process of calculating the land surface emissivity in Step 2 is as follows: (1) Calculate the normalized difference vegetation index NDVI using visible and near-infrared data, the formula is as follows: where ρ 1 and ρ 2 are the reflectance values of the visible and near-infrared bands 1 and 2 of FY3 VIRR, respectively; (2) Further calculate the vegetation coverage through the NDVI calculated in (1), the formula is as follows: Where P v is the vegetation coverage, NDVI v is the NDVI value of the area completely covered by vegetation, that is, the NDVI value of pure vegetation pixels, and NDVI s is the NDVI value of the area completely bare soil or without vegetation coverage; (3) Further calculate the land surface emissivity through the NDVI and FVC calculated in (1) and (2), the formula is as follows: ε i = P v R v ε iv +(1 - P v )R s ε is + d ε where ε 4v = 0.98672; ε 5v = 0.98990; ε 4s = 0.96767; ε 5s = 0.97790, R v and R s are the temperature ratios of vegetation and bare soil respectively, and the calculation formulas are as follows: R v = 0.9332 + 0.0585P v R s = 0.9902 + 0.1068P v When there is a large difference in height on the ground surface, d can be taken as ε 0; if the ground surface is uneven, it can be simply estimated according to the composition ratio of vegetation: when P v ≤ 0.5, d ε = 0.0038P v ; when P v > 0.5, d ε = 0.0038(1 - P v ); when P v = 0.5, d ε is the largest, d ε = 0.0019; The process of calculating the land surface temperature in Step 3 is as follows: T s = -0.143 + P(T 4 + T 5 ) / 2 + M(T 4 - T 5 ) / 2 where T s is the surface temperature, which is calculated from the parameter brightness temperature T 4 and T 5 , surface emissivity ε 4 and ε 5 and is further calculated as follows: The specific calculation formula is as follows: P = 1 + 0.122(1 - ε) / ε - 0.061Δε / ε 2 M = 5.393 + 7.702(1 - ε) / ε - 3.876Δε / ε 2 ε = (ε 4 + ε 5 ) / 2 Δε=(ε 4 -ε 5 ) / 2 Among them, T 4 is the brightness temperature of the 4th channel of FY3 VIRR, T 5 is the brightness temperature of the 5th channel, ε 4 is the surface emissivity of the 4th channel, ε 5 is the surface emissivity of the 5th channel.

2. A land surface temperature retrieval system using the method for retrieving land surface temperature from FY3 VIRR data according to claim 1.

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