NDBI简介及计算
Normalized Difference Built-up Index (NDBI)
⽤来分析建成区的指数有很多：
Normalized Difference Built-up Index (NDBI)
Built-up Index (BU)
Urban Index (UI)
Index-based Built-up Index (IBI)
Enhanced Built-up and Bareness Index (EBBI)
这些是最常⽤的，它们有各⾃的计算⽅法. 建成区和裸⼟在SWIR(短波红外)波段⽐在NIR(近红外)波段反射更多⼀些. ⽔体在红外波段⼏乎没有反射。
For better result, you can use Built-up Index (BU). Build-up Index is the index for analysis of urban pattern using NDBI and NDVI. Built-up index is the binary image with only higher positive value indicates
built-up and barren thus, allows BU to map the built-up area automatically.
BU = NDBI - NDVI
NDBI 计算：
NDBI = (SWIR – NIR) / (SWIR + NIR)
For Landsat 7 data, NDBI = (Band 5 – Band 4) / (Band 5 + Band 4)
For Landsat 8 data, NDBI = (Band 6 – Band 5) / (Band 6 + Band 5)
Also, the Normalize Difference Build-up Index value lies between -1 to +1.
NDBI 负值代表⽔体，⾼值代表建成区，植被的NDBI值⽐较低。
ENVI中Band Math计算公式：float(b5-b4)/float(b5+b4)  或者 (float(b5)-float(b4))/(float(b5)+float(b4))
float up