Overview

Convert Orbita Level-1 Zhuhai-1 satellite data to TOA reflectance

欧比特珠海一号高光谱数据 Level-1原始数据转表观/行星反射率

Note: the output file is TOA reflectance*10000

Such formmating is inline with Landsat-8 and Sentinel-2 to save space

Feel free to contact me for further information: liushengjie0756 [AT] gmail.com

Motivation and Goal

The Zhuhai-1 hyperspectral satellite imagery did not provide offical TOA reflectance data
The level-1 data are raw data with method for radiometric calibration, which can covert the raw data to TOA radiance
TOA radiance is an observation that reflects both energy density of the ground target and the sun
To eliminate the effect of sun and covert radiance to reflectance, we need to calculate how strong the sum is on top of atmosphere
To do so, we need a solar irradiance spectrum. Then, we can convert radiance to reflectance by the following formula
(pi * L * square(d) * cos(theta)) / ESUN

where L is radiance, d is the local Earth-Sun distance in astronomical units, theta is solar zenith angle in degrees, and ESUN is the calculated mean solar exoatmospheric irradiances.

The ESUN file of Zhuhai-1 Hyperspectral Sensors

Various solar spectrum are available.
In my implementation, the 1985 Wehrli Standard Extraterrestrial Solar Irradiance Spectrum is chosen because it is the first spectrum that came to my eyes.
A set ot the ESUN values of Zhuhai-1 hyperspectral sensors is provided here as esun_obt.xlsx

Usage

unzip all the Zhuhai-1 hyperspectral data to one directory (path)
change all three arguments in the script

three arguments

path: the one directory saving all the hyperspectral data
esunfile: obt_esun.xlsx file
outputpath: output data location

To do