在熬了两夜，整整两天连登陆学校邮箱都顾不上的不断 scripting 和 debug 之后，我总算完成了研究地区的一部分净初级生产力分布图。
2007年12月6日星期四
A flavour of AVHRR
In the past few days I have been trying to find suitable software and process for AVHRR data processing. The METOP AVHRR format looks like an enigma. It should be compatible to AVHRR, but despite that I tried hard to find a tool to unpack the file, and even tried to write a Fortran program myself, I couldn't find anything that decodes the file downloaded from [CLASS](http://www.class.noaa.gov/).
What made the search not totally fruitless is a image processing tool, [BEAM](http://www.brockmann-consult.de/beam/), which works nicely with AVHRR and a number of other data files. I can use it to open AVHRR 16-bit and 8-bit Level 1b file (10-bit not tested yet), do some simple preprocessing and statistics, then export the file as GeoTIFF or other formats, which can be read by GRASS GIS + GDAL. It is worth noting that BEAM is free as in free speech software published under GPL **v3** and can run on any platform with Java Runtime Environment.
With the help of BEAM and GRASS I managed to produce my first AVHRR-derived NDVI image this afternoon. Seems I am finally on track. In the coming days there are a number of things that I can look at:
- AVHRR Pathfinder data, their advantages and limits, suggested by one of my supervisor;
- Snow and ice cover mapping with AVHRR;
- Time series data and change detection;
- MODIS data and its interoperability with AVHRR.
What made the search not totally fruitless is a image processing tool, [BEAM](http://www.brockmann-consult.de/beam/), which works nicely with AVHRR and a number of other data files. I can use it to open AVHRR 16-bit and 8-bit Level 1b file (10-bit not tested yet), do some simple preprocessing and statistics, then export the file as GeoTIFF or other formats, which can be read by GRASS GIS + GDAL. It is worth noting that BEAM is free as in free speech software published under GPL **v3** and can run on any platform with Java Runtime Environment.
With the help of BEAM and GRASS I managed to produce my first AVHRR-derived NDVI image this afternoon. Seems I am finally on track. In the coming days there are a number of things that I can look at:
- AVHRR Pathfinder data, their advantages and limits, suggested by one of my supervisor;
- Snow and ice cover mapping with AVHRR;
- Time series data and change detection;
- MODIS data and its interoperability with AVHRR.
2007年10月22日星期一
Preliminary Image Availability Survey
I am looking for satellite images over Anduo County, Tibet Autonomous Region, China.
- AVHRR： Search at EarthExplorer gives 11577 images in daylight condition, most focus on Indian subcontinent, but should be enough for me. Dates are from 1980 to 2000s.
- Declassified Satellite Imagery-1: Low and medium images taken in 1960s, earliest 1961, from CORONA, ARGON and LANYARD satellites. Most are medium to low resolution (15-30 m). A large portion are cloudy. $30 per frame.
- Declassified Satellite Imagery-2: Much higher camera resolution at 2 to 4 feet and 20 to 30 feet, from KH-7 and KH-9. Taken in 1964-1965 and 1973. Large swath, relatively lower cloud mask. $30 per frame.
- EO-1: no images.
- Landsat 1-5 MSS: From 1972 to 1992. Some scan line can be seen. Less cloud. $200 per frame.
- Landsat 4-5 TM: July 1982 to Present. Good resolution, less cloud. $425 per frame.
- Landsat 7 ETM+ International Ground Stations: No reviews available. No uniform price.
- Landsat 7 ETM+: From 1999 to 2003, some are a bit cloudy. Most are usable. $475-600 per frame.
- Landsat 7 ETH+ SLC-off: More difficult to process and probably data loss. From 2003 to Present. Can be downloaded with ordering. $200-275 per frame.
Landsat 7 ETM+ scenes acquired from 5/31/03 - 7/14/03 and 9/3/03 - 9/17/03 are not available. - SPOT: no image from USGS.
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