# 「教程」遥感图像预处理之辐射定标

## 步骤一 加载文件

MultiSpectral多光谱数据（1~7波段）

Panchromatic 全色波段数据（8波段）

Cirrus卷云波段数据（9波段）

Thermal热红外数据（10，11波段）

Quality质量波段数据（12波段）

## 步骤二 调用辐射定标工具

correction和calibrate意思相近，区别在哪里，牛津字典上是这样解释的

correction: a change that makes sth more accurate than it was before

calibrate: to mark units of measurement on an instrument such as a thermometer so that it can be used for measuring sth accurately.

## 步骤四 设置参数

1. 多光谱数据可以进行辐射率定标和反射率定标；

2. 热红外数据可以进行辐射率定标和亮度温度定标。

## 步骤五 输出结果

Output Filename下选择输出路径和文件名，以.dat格式输出，点击OK执行处理。

## 原理探究

Radiance: This option is available if the image has gains and offsets for each band. ENVI reads these values from metadata from the sensors listed above. Radiance is computed using the following equation:

$L_{\lambda}=Gain * Pixel value + Offset$

ENVI expects gains and offsets to be in units of W/(m2 * sr * µm). If so, then radiance will be in units of W/(m2 * sr * µm).

ENVI期望增益和偏移的单位为W/(m2 * sr * µm) 这样的话，辐射率的单位就为W/(m2 * sr * µm)

Reflectance: Top-of-atmosphere reflectance (0 to 1.0). This option is available if the image has gains, offsets, solar irradiance, sun elevation, and acquisition time defined in the metadata. ENVI reads these values from metadata from the sensors listed above. Reflectance is computed using the following equation:

$$\rho_{\lambda} = \ \frac{\pi L_{\lambda}d^{2}}{\text{ESUN}_{\lambda}\sin\theta}$$

With Landsat-8 files, the reflectance gains and offsets have been scaled by the sine of the sun elevation.

Landsat-8数据中，反射率增益和偏移量已经按太阳高度角正弦值进行了缩放。

Brightness Temperature: This option is only available for Landsat-8, ETM+, and TM thermal imagery. Brightness temperatures (in Kelvin) are computed as follows:

$$T = \ \frac{K2}{\ln{(\frac{K1}{L_{\lambda}} + 1)}}$$

K1 and K2 = Calibration contstants, in Kelvin. ENVI reads these values from the Landsat metadata. 其中K1和 K2为定标常量，ENVI会从元数据中读取。

## 其他参数下的结果

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