ICESat data download
1. Introduction to ICESat
In 2003, NASA (National Aeronautics and Space Administration) of the United States launched the ice, cloud and land elevation satellite ICESat. The Earth Science Laser Altimeter System GLAS carried on it is the world's first laser radar system for continuous observation of the earth. Used to monitor elevation changes in the ice sheets of Antarctica and Greenland, measure cloud height and cloud/aerosol vertical structure on a global scale, and forest vertical structure information.
The satellite was launched in 2003 and ended its observation mission in 2009, during which it obtained a large amount of observation data. There are 15 categories of data products, named as GLAS01-GLAS15, which are divided into three levels of data: level 0, level 1 and level 2, of which L1 level data is further divided into two levels of data: L1A and L1B. L0 is the original telemetry waveform packet data recorded in chronological order; L1A is the original data with full resolution based on time series without data processing; L1B level data is the L1A level data after device correction, data processing, based on attitude and position The data is formed by laser foot point positioning; L2 level data is more accurate after LIB level data has been processed by various corrections, and is divided into elevation and position data of different surface types, as well as various distance and elevation corrections. Fix data. The technical index parameters of ICESat/GLAS are as follows.
2. ICESat data products
ICESat satellite data products are generated by I-SIPS (ICESAT Science Investigator-led Processing System) of Goddard Space Flight Center. According to the echo information received by GLAS, various physical parameters are extracted, and 15 categories of standard data products can be obtained. The naming method for GLA01-GLA15. The system data files are published by the National Snow and Ice Data Center, Distributed Active Archive Center, NASANSIDC DAAC.
GLAS data products are stored in units of days and recorded in the form of binary integers. Each data file contains multiple elements, and the length of each element is fixed at 4 bytes. If there are not enough 4 bytes, it needs to be filled. The laser pulse conforms to the time sequence in the process of emission and propagation, so the laser pulse received first by the receiver corresponds to the detection target closest to the satellite, and the last pulse signal received indicates that the target is farthest from the detector. The data records are in time series, and the data description starts with the header file, including the length of the data file and the number of months in the header file.
2.1 GLA01 data
The content in the GLA01 data file is divided into three parts. The record type "0" indicates the main record data, "1" indicates the 1064nm long-wave record data, and "2" indicates the 532nm short-wave record data. Except for the data directly related to the echo waveform, the rest of the laser pulse altimetry information is included in the main record data. The long-wave record data records the land echo waveform, including 544 echo information sampling points and related data. The short-wave recording data records the ocean surface echo waveform, including 200 echo information sampling points and other relevant data.
2.2 GLA14 data
GLA14 data is the L2 level data generated by the combination of GLA05 and GLA06 data, and records the final data processing results of the land surface of the altimetry system. These include the geodetic latitude and longitude of the laser foot point, the geodetic height, the elevation available marker, the saturation correction marker and the pulse gain and other parameters.
3. Data download
NSIDC official website: https://nsidc.org/home
Step 1:
Search data: https://nsidc.org/data/explore-data
Step 2: Select the data product to be downloaded
Step 3: You can use wget, earthdata or Browser to browse and download. Which one to use depends on your choice.
Data download method tutorial: https://nsidc.org/data/user-resources/help-center/programmatic-data-access-guide
(1) EarthData data download
(2) Download via browser, download link: https://n5eil01u.ecs.nsidc.org/GLAS/ , you can use wget, python or downthemall for batch download.
4. Summary
ICESat-2 download method is the same as above.