一、介绍
系统采用的云检测算法是多光谱综合去云法。该算法从可见光反射率、红外波段亮温值以及亮温差等方面综合考虑，逐步建立一个云检测掩膜。对于预测的MODIS数据必须是经过了辐射定标的，热辐射强度转换成了亮温的。多光谱综合去云算法用到的波段以及算法流程见下图。
二、IDL源码
;+
;:Description:
; Describe the procedure.
;
;:Author: tiands@esrichina.com.cn
;
;:Date: 2013-9-5 11:10:27
;-
;;=======================================================================
;;; 该程序对几何校正后的科学数据进行去除云处理
;;;======================================================================
PRO MODIS_CLOUD,filename,out_name,outname_cloud
COMPILE_OPT idl2
ENVI, /RESTORE_BASE_SAVE_FILES
ENVI_BATCH_INIT, LOG_FILE = 'batch_log.txt'
; filename='C:\Users\tiandeshan\Desktop\idl\scaledata.img'
; out_name='C:\Users\tiandeshan\Desktop\idl\scaledata_cloud.img'
;数据读取
IF (ENVI_IS_GDB(filename)) THEN BEGIN
ENVI_OPEN_GDB,filename,r_fid=data_fid
ENDIF ELSE BEGIN
ENVI_OPEN_FILE,filename,r_fid=data_fid
ENDELSE
;envi_open_file, filename, r_fid=data_fid
ENVI_FILE_QUERY, data_fid, dims=dims, nb=nb,ns=ns,nl=nl,data_type =data_type
data = MAKE_ARRAY(ns,nl,nb,type=data_type)
FOR i=0,nb-1 DO BEGIN
data[*,*,i]=ENVI_GET_DATA(fid=data_fid,pos=i,dims=dims)
ENDFOR
;不同波段不同条件多次判断出各种云
cloud_1=data[*,*,0] GT 0.3
cloud_2=data[*,*,8] GT 0.008 AND [data[*,*,9]-data[*,*,10]] GT -0.012
cloud_3=data[*,*,8] GT 0.02 AND data[*,*,0] LE 0.2
cloud_4=data[*,*,8] LT 0.02 AND data[*,*,0] GT 0.2
cloud_5=data[*,*,6] GT 0.17 AND (-0.0009) LT (data[*,*,0]-data[*,*,4])/(data[*,*,0]+data[*,*,4]) LT 0.002 AND data[*,*,0] GT 0.2
cloud_all=cloud_1 OR cloud_2 OR cloud_3 OR cloud_4 OR cloud_5
cloud_data=(cloud_all EQ 0)*1
map_info=ENVI_GET_MAP_INFO(fid=data_fid)
ENVI_WRITE_ENVI_FILE, cloud_data,r_fid=mask_fid,out_name=outname_cloud,map_info=map_info
CLOUD_MASK,data_fid,mask_fid,out_name
ENVI_BATCH_EXIT
END
PRO CLOUD_MASK,data_fid,mask_fid,out_name
COMPILE_OPT IDL2
ENVI_FILE_QUERY,data_fid,nb=nb,dims=dims
pos = [0,1,2,3,4,5,7,10,11]
m_pos = [0]
;判断是否传入了out_name
IF (not KEYWORD_SET(out_name)) THEN BEGIN
IN_MEMORY=1
ENDIF ELSE BEGIN
IN_MEMORY=0
ENDELSE
OUT_BNAME=['cloud_mask(1KM Reflectance (band1) [250 Aggr])','cloud_mask(1KM Reflectance (band2) [250 Aggr])',$
'cloud_mask(1KM Reflectance (band3) [500 Aggr])','cloud_mask(1KM Reflectance (band4) [500 Aggr])','cloud_mask(1KM Reflectance (band6)[500 Aggr]',$
'cloud_mask(1KM Reflectance (band7)[500 Aggr]','cloud_mask(1KM Reflectance (band19))',$
'cloud_mask(1KM Emissive (band31))','cloud_mask(1KM Emissive (band32))']
ENVI_MASK_APPLY_DOIT, FID = data_fid, POS = pos, DIMS = dims, $
M_FID = mask_fid, M_POS = m_pos, VALUE =0, $
out_bname=OUT_BNAME,$
IN_MEMORY = IN_MEMORY, R_FID =m_fid , OUT_NAME = out_name
END
