MOD09A1数据下载与与处理-地表干湿度指数的计算

Posted 2021-11-23 空中旋转篮球

1.MOD09A1数据介绍

1.1 数据介绍网址：LP DAAC - Search

中分辨率成像光谱仪 (MODIS) Terra MOD09A1 6.1 版产品提供了对 Terra MODIS 波段 1 至 7 的表面光谱反射率的估计，并针对大气条件（如气体、气溶胶和瑞利散射）进行了校正。 除了七个 500 米 (m) 反射带之外，还有两个质量层和四个观测带。 对于每个像素，从 8 天合成周期内的所有采集中选择一个值。 像素选择的标准包括云天顶和太阳天顶。 当多次采集满足标准时，使用具有最小通道 3（蓝色）值的像素。（原文：he Moderate Resolution Imaging Spectroradiometer (MODIS) Terra MOD09A1 Version 6.1 product provides an estimate of the surface spectral reflectance of Terra MODIS Bands 1 through 7 corrected for atmospheric conditions such as gasses, aerosols, and Rayleigh scattering. Along with the seven 500 meter (m) reflectance bands are two quality layers and four observation bands. For each pixel, a value is selected from all the acquisitions within the 8-day composite period. The criteria for the pixel choice include cloud and solar zenith. When several acquisitions meet the criteria the pixel with the minimum channel 3 (blue) value is used.）

1.2 波段信息

SDS Name	Description	Units	Data Type	Fill Value	No Data Value	Valid Range	Scale Factor
sur_refl_b01	Surface Reflectance Band 1 (620-670 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b02	Surface Reflectance Band 2 (841-876 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b03	Surface Reflectance Band 3 (459-479 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b04	Surface Reflectance Band 4 (545-565 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b05	Surface Reflectance Band 5 (1230-1250 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b06	Surface Reflectance Band 6 (1628-1652 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_b07	Surface Reflectance Band 7 (2105-2155 nm)	N/A	16-bit signed integer	-28672	N/A	-100 to 16000	0.0001
sur_refl_qc_500m	Surface reflectance 500m band quality control flags	Bit Field	32-bit unsigned integer	4294967295	N/A	0 to 4294966531	N/A
sur_refl_szen	MODIS solar zenith angle	Degree	16-bit signed integer	0	N/A	0 to 18000	0.01
sur_refl_vzen	MODIS view zenith angle	Degree	16-bit signed integer	0	N/A	0 to 18000	0.01
sur_refl_raz	MODIS relative azimuth angle	Degree	16-bit signed integer	0	N/A	-18000 to 18000	0.01
sur_refl_state_500m	Surface reflectance 500m state flags	Bit Field	16-bit unsigned integer	65535	N/A	0 to 57343	N/A
sur_refl_day_of_year	Day of the year for the pixel	Julian day	16-bit unsigned integer	65535	N/A	1 to 366	N/A

2 数据下载与处理

2.1 下载地址

 地址：LAADS DAAC

数据产品类型、时间、位置等参数设置 进行数据查询。

查询到合适的数据即可进行直接下载或者批量下载。

2.2 数据预处理（投影和格式转换）

采用MRT工具将原始HDF数据转化为albers投影下的TIFF数据。

处理结果：

 

 3 干湿度指数计算

3.1 湿度指数Wet计算

计算公式：

WET-MOD09A1=0.1147*RED+0.2489*NIR1+0.2408*BLUE+0.3132*GREEN-0.3122*NIR2 -0.6416*SWIR1-0.5087*SWIR2

(0.1147*B1+0.2489*B2+0.2408*B3+0.3132*B4-0.3122*B5 -0.6416*B6-0.5087*B7)

1-RED,2-NIR1,3-BLUE,4-GREEN,5-NIR2,6-SWIR1,7-SWIR2；

 blue (459–479 nm), green (545–565 nm), red(620–670 nm), near infrared (NIR1: 841–875 nm; NIR2:1230–1250 nm), and shortwave infrared (SWIR1: 1628–1652 nm, SWIR2: 2105–2155 nm)

使用ENVI Band Math工具直接计算。

 3.2 干度指数（NDBSI）计算

计算公式：

干度指数（NDBSI）由城市建筑指数（IBI）和裸土指数（SI）的平均值得到的，该指数的范围是[-1,1]，值越大，表示越干燥。

其中，ρblue、ρgreen、ρred、ρnir、ρswir1分别表示蓝、绿、红、近红外、中红外1

在Band math中输入公式为：

SI = (float((b3+b5)-(b1+b4)))/((b3+b5)+(b1+b4))

IBI=((float(2*b5))/(float(b5+b4))-((float(b4))/(float(b4+b3))+(float(b2))/(float(b2+b5))))/((float(2*b5))/(float(b5+b4))+                              ((float(b4))/(float(b4+b3))+(float(b2))/(float(b2+b5))))   

其中，b1~b5分别为蓝、绿、红、近红外波段、中红外波段1.

            NDSI = （b1+b2)/2   其中，b1、b2分别为IBI图像、SI图像。