LCF

IDL procedures for calculating Low Cloud Frequency (LCF) from the MODIS Cloud Product

Instructions

Data preparing

1. Run check_hdf.pro to make sure that all downloaded MOD/MYD35 Cloud Mask and MOD/MYD03 Geolocation files are correct. If there exist any broken HDF files, the procedure will write those file names to a log file named [dir].redownload.txt. Redownload those files and rerun the procedure until no entry in the log file.
2. Run gen_prm_bat_file.pro to generate MRTSwath parameter files for each MOD/MYD35 file and a batch file named mrtswath.bat. Prior to running mrtswath.bat you will need to ensure that you have installed MRTSwath and added the bin directory of MRTSwath to PATH environment variable on your system.
3. Run check_mrtswath_georef.pro to check whether there are any MOD/MYD35 files that MRTSwath failed to georeferece maybe due to Fill Value. The procedure will generate a log file named MRTSwathFail.txt and copy all unsuccesfully georeferenced MOD/MYD35 and MOD/MYD03 files to MRTSwathFail directory for step 4 processing. If MRTSwath successfully georeferenced all files, skip step 4.
4. Run georef_mod35_using_mod03.pro to geoference those unsuccesfully georeferenced files in step 3. Pay attention to that the results of this procedure are a bit different from MRTSwath in pixel size. If anyone knows MRTSwath how to calculate output pixel size, please tell me.

Data preprocessing

1. Run detect_lc_from_mod35.pro to detect low cloud from MOD/MYD35 Cloud Mask. The cloud classification scheme is: 0 - background, 1 - pure low cloud, 2 - obscure, 3 - no low cloud and 4 - probable low cloud (1 or 2).
2. Run resize_mod35_lc.pro to resample all low cloud image to same pixel size. It's an essential step before gettting the following step 3 correctly execution.
3. Run mosaic_mod35_lc.pro to combine multiple images into a single seamless composite image that completely covers the study area for day (0) or night (1).
4. Run subset_mod35_lc.pro to subset the mosaicking image via the shapefile of study area.

LCF calculation

1. Run calc_mod35_lcf.pro to calculate pure low cloud frequency, obscure frequency, no low cloud frequency and probable low cloud frequency. The corresponding band names of resulting images are Monthly LCF1, Monthly OF, Monthly NLCF and Monthly LCF2.

LCF extraction

1. Run get_mod35_lcf_via_evf.pro to extract the LCF of ROI storing in an ENVI evf file to txt file for further analysis in R.

Publications

The procedures are developed for following studies.

[1] Lu, H., Zhang, Y., & Cai, J. (2015). Consistency and differences between remotely sensed and surface observed total cloud cover over China. International Journal of Remote Sensing, 36(16), 4160-4176.

[2] Zhang, Y., Lu, H., & Cai, J. (2014, November). Towards the comparison of satellite and ground based cloud amount over China. In SPIE Asia Pacific Remote Sensing (pp. 92590A-92590A). International Society for Optics and Photonics.

[3] Zhang, Y., Lu, H., & Cai, J. (2014, July). Estimating regional amount of low clouds over North China plain from multi-source remote sensing data. In 2014 IEEE Geoscience and Remote Sensing Symposium (pp. 4131-4134). IEEE.