Sunday, January 24, 2010

Aqua Satellite Data Processing

In this post we look at the steps that go into processing the Aqua satellite data. We'll be looking at Level 0 (raw satellite) data to level 2A data.

Additional Posts In This Series
A Note On The UAH And RSS Raw Data
How UAH And RSS Temperatures Are Measured
Overview Of The Aqua Satellite
Looking At The Aqua Satellite Data
UAH Satellite Data.html
Dangit! More Climate Stuff. UAH and RSS Raw Data

Level 0 data is the actual data produced by the instruments on the satellite. The data has not been through Quality Assurance, it hasn't been geocoded, etc.

I'm not going to be using data at such a low level, but if you want to download it, the University of Wisconsin keeps the last four days of Level 0 data for the Aqua satellite here. Connect via FTP as an anonymous (Guest) user. See the file 00README.txt for additional information.

Level 0 AMSR-E data is processed into Level 1A data by the Japan Aerospace Exploration Agency (JAXA). Level 0 AMSU data is processed into Level 1A data by NASA. Like Level 0 data, I consider Level 1A data too low level to use.

AMSU Level 1A data contains geo-located data counts and engineering parameters. I have not been able to find AMSU Level 1A data online for downloading.

For AMSR-E Level 1A data, each half-orbit data granule consists of observation counts, antenna temperature coefficients, offsets for calculating antenna temperatures, calibration temperature counts, land/ocean flags, time, latitude, longitude, and navigation fields in HDF format. The data sampling interval is 2.6 msec for each 1.5-sec scan period for the 6.9-GHz to 36.5-GHz channels, and 1.3 msec for the 89.0-GHz channel. AMSR-E collects 243 data points per scan for the 6.9-GHz to 36.5-GHz channels, and 486 data points for the 89.0-GHz channel. Each swath spans 50 minutes.

AMSR-E Level 1A data can be downloaded here.

Level 1A AMSR-E data is processed into Level 1B data by the Japan Aerospace Exploration Agency (JAXA). Level 1A AMSU data is processed into Level 1B data by NASA.

The AMSU-A Level 1B data set contains AMSU-A calibrated and geolocated brightness temperatures in degrees Kelvin. This data set is generated from AMSU-A Level 1A digital numbers (DN) and contains 15 microwave channels in the 50 - 90 GHz and 23 - 32 GHz regions of the spectrum. A day's worth of data is divided into 240 scenes, each of 6 minute duration. An AMSU-A scene contains 30 cross-track footprints in each of 45 along-track scanlines, for a total of 45 x 30 = 1350 footprints per scene. The AMSU-A is co-aligned with the AIRS instrument onboard the Aqua platform so that successive blocks of 3 x 3 AIRS footprints are corresponding to AMSU-A footprint. The AMSU Level 1B data can be downloaded from the NASA AIRS data holdings web page. A Quick start Guide for this data is here. Code for reading Level 1B data is available for IDL, MATLAB, Fortran, and C.

AMSR-E Level 1B data is brightness temperature that is transformed from antenna temperature in level 1A by transformation coefficients. The JAXA link to the AMSR-E Level 1B data is a dead link.

Level 2A data is created from Level 1B data by either RSS or NASA. Level 2A data contains derived data and is used to produce various Level 3 and Level 4 data files.

AMSU Level 2A data contains combined data from the AIRS/AMSU/HSB instruments and can be downloaded here.

AMSR-E Level 2A data is brightness temperature that contains derived geophysical variables at the same resolution and location as the Level-1 source data. These derived data include geophysical quantities for water, water vapor, cloud liquid water, precipitation, sea surface wind speed , sea surface temperature, sea ice concentration, snow water equivalent, and soil moisture.

Recently the AMSR-E/Aqua Level 2A data was determined to have errors in the resampled 89.0 GHz Horizontal (H) fields. Files with data coverage from 19 June 2002 00:29 through 4 November 2004 05:43 are affected. The fields containing bad data are:
• 89.0H_Res.1_TB
• 89.0H_Res.2_TB
• 89.0H_Res.3_TB
• 89.0H_Res.4_TB

AMSR-E Level 2A data can be downloaded here.

An online history of of the changes made to processing this data can be found here.

Guide Documents for AIRS Version 5 Products
University of Wisconsin Aqua Satellite Level 0 Data
AMSR-E/Aqua L1A Raw Observation Counts
Aqua Project Science Data Products Summary
NSIDC Data Pool
AMSR-E Format L2
JAXA/EOC (Dead Link)
NASA AIRS data holdings web page
AIRS/AMSU/HSB Version 5 Level 1B QA Quick Start
IDL AMSU Level 1B Swath and Grid Readers
MATLAB AMSU Level 1B Swath and Grid Readers
Fortran AMSU Level 1B Swath and Grid Readers
C AMSU Level 1B Swath and Grid Readers
NSIDC AMSR-E Data Frequently Asked Questions
AMSR-E Level 2 Map format description (NDX-000273D)
EOS Data Pool @ NSIDC AMSR-E Level 2A Data Download.
AMSR-E L2A Brightness Temperatures: Bad Resampled 89 GHz Horizontal Data
AMSR-E Data News


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