Description of AMSR Data Products

Version Notes Introduction AMSR-E Data AMSR-J Data Geophysical Data Products Graphic Image Maps Gridded Binary Data Files Acknowledgement

Version-5 AMSR-E Ocean Products - February, 2006

On February 8, 2006, the AMSR-E ocean products were updated to Version-5.

Version-5 represents a major update to the AMSR-E processing algorithm. The changes that were made relative to the previous Version-4 are summarized below and further details are given.

1. Improvements to the geolocation routines have been made. The latitudes and longitudes for the geophysical retrievals are now more accurate. Due to a previously undetected misalignment of the AMSR-E sensor mounting on the Aqua spacecraft, errors in Version-4 were as large as 5-10 km. For Version-5, the accuracy is estimated to be within 1 to 3 km.

2. A correction has been applied to remove moon contamination in the AMSR-E cold mirror.

3. Improvements have been made to the AMSR-E rain rates, with an overall effect of reducing the rain rates substantially in the tropics.

4. Near-real time bytemaps and imagery that are normally about 3 hours behind observation are now available, although we still expect occasional delays in receiving or processing data. This represents a decrease in data latency of 12 to 16 hours relative to the Version-4 products. The near-real time bytemap names contain "rt" where "v5" appears in the final bytemap names. We expect the rt and final versions to look similar; however, the rt files are not intended for climate studies and should not be archived.

A small change was made to the data file format of the rain product, but the change has been reverted as of 2006-Sept-20.

The bytemap folder name has changed to "bmaps_v05" and the file version designation has changed to "v5."

Further details on these Version-5 changes

Even more detail on brightness temperature calibration changes affecting this version update

Introduction

The Advanced Microwave Scanning Radiometer (AMSR-E) was launched on May 4, 2002, aboard NASA’s Aqua spacecraft. The National Space Development Agency of Japan (NASDA) provided AMSR-E to NASA as an indispensable part of Aqua’s global hydrology mission. Over the oceans, AMSR-E is measuring a number of important geophysical parameters, including sea surface temperature (SST), wind speed, atmospheric water vapor, cloud water, and rain rate. A key feature of AMSR-E is its capability to see through clouds, thereby providing an uninterrupted view of global SST and surface wind fields.

The AMSR-E Ocean Products produced for this website are made using a modified version of the ASMR-E Direct Broadcast (DB) algorithm developed for NASA. We are using an on-orbit calibration method developed here at RSS to convert counts to brightness temperatures. Calibration methodology and preliminary validation results are described in the following paper:

"On-Orbit Calibration of AMSR-E and the Retrieval of Ocean Products"	PDF format

AMSR-E Data

The RSS AMSR-E geophysical dataset consists of data derived from observations collected by the AMSR-E instrument carried on board the Aqua satellite.

Remote Sensing Systems performs a detailed processing of AMSR-E instrument data in two stages.

The first stage produces a near-real-time (NRT) product (identified by "rt" within the file name) which we make available as soon as possible. This is generally within 3 hours of when the data are recorded, except for occasional delays in receiving or processing data. Although suitable for many timely uses, and the differences may appear subtle, the NRT products are not intended to be archive quality. They will be deleted within several days and should not be archived.

"Final" data (identified by "v5" within the file name) are processed when we receive the NCEP FNL analysis. The NCEP wind directions are particularly useful for retrieving more accurate SSTs and wind speeds. The final "v5" products will continue to accumulate new swaths (half orbits) until the maps are full, generally within 2 days. Occasionally, data become available after more lengthy delays, and such data will be added to final "v5" products. Thus, final refers to the type of swath processing, and does not imply that a data file is finalized (as in, will not change). Newly available data swaths will be added to final "v5" products.

Browse imagery will display NRT ("rt") data while it is available, final data thereafter.

AMSR-J Data

AMSR-J stands for AMSR flown by JAXA on Midori-II (renamed from ADEOS-II after launch).

AMSR-J recorded data on 237 days in 2003 (January through October).
There are many gaps within the AMSR-J data set.
Please use the browse imagery or FTP site to determine specific availability.

Differences between AMSR-E and AMSR-J:

	AMSR-E	AMSR-J
Platform	AQUA	Midori-II
Altitude	705 km	802.9 km
Equator Crossing Time (Local time zone)	1:30 PM Ascending 1:30 AM Descending	10:30 PM Ascending 10:30 AM Descending
Antenna Size	1.6 m	2 m
Swath Width	1450 km	1600 km

The wider swath of AMSR-J provides greater coverage, but comes at the expense of accuracy near the swath edges. Here is a worst case example:

AMSR-J swath edge artifacts are only obvious in SST, and are most prominent early in the mission, when the spacecraft position was most unstable and least accurately known.

Geophysical Data Products

Sea Surface Temperature (SST)	temperature of the top layer (skin) of water approximately 1 milimeter thick missing due to:   high wind speed (> 20 m/s);   sun glint;   rain; near sea ice;   near land (~75km)
Surface Wind Speed (WSPD)	wind speed 10 meters above the water surface, derived from surface roughness (wind stress) missing due to:   sun glint;   rain;   near sea ice;   near land (~50km)
Atmospheric Water Vapor (VAPOR)	total gaseous water contained in a vertical column of atmosphere missing due to:   heavy rain;   near land (~25km)
Cloud Liquid Water (CLOUD)	total cloud liquid water contained in a vertical column of atmosphere does not include rain or solid water (snow, ice) missing due to:   near land (~25km)
Rain Rate (RAIN)	rate of liquid water precipitation does not include solid water (snow, ice) missing due to:   near land (~25km)

Daily and Time Composite Data

Gridded data are organized according to observation date. All dates and times are Coordinated Universal Time (UTC), also known as Greenwich Mean Time (GMT), Zulu Time (Z), Universal Time (UT), and World Time.

Data products include daily and time averaged geophysical data as follows:

Daily	orbital data mapped to 0.25 degree grid divided into 2 maps based on ascending and descending passes early data may be overwritten by later data at high latitudes and daily "seam"
3-Day	average of 3 days ending on and including file date
Weekly	average of 7 days ending on and including the Saturday file date
Monthly	average of all data within the calendar month

Missing Data

There are gaps within these data. Missing data generally affects Daily and 3-Day products, but can also reduce the number of observations in Weekly and Monthly averages.

When browsing imagery, the navigation may skip dates with no data, or you may see a blank map stating that no data is available for that time.

Binary data files for dates with completely missing data are not produced; they will be absent from our FTP server.

Data gaps are generally due to missing data upstream from our processing facility, such as the instrument being turned off. Occasionally, there are delays in obtaining and/or processing recently recorded data; beyond several weeks, it is unlikely that missing data will become available.

Dates for which AMSR-E data are completely missing include:

Graphic Image Maps

Each daily, 3-day, weekly and monthly graphic image map displays one geophysical parameter: Sea Surface Temperature (SST), 10 meter Surface Wind Speed (WSPD), Columnar Water Vapor (VAPOR), Cloud Liquid Water (CLOUD), or Rain Rate (RAIN). The daily maps display the daytime or nighttime satellite passes separately. The date of the data displayed is the UTC date when the data were collected. The scale for each map is located next to the map for reference. The scale bar extends between zero (-1 for sst) and the defined maximum listed below:

White areas on the daily map represent regions of ice (greater than 0% sea ice) as determined by the AMSR-E instrument. In the time-averaged maps, ice is indicated when ice is present over 50% of the time, or when the number of times a cell is identified as containing ice is greater than the number of times the cell contains data. Land regions are colored gray. Those areas where AMSR-E data are not available are black. The black color includes areas where the satellite did not pass over and no data were collected, areas where data were collected but were determined to be bad, coastal areas, areas affected by sun glint on the SST and wind speed maps, areas near sea ice on the SST and wind speed maps, areas of rain on the SST and wind speed maps, areas of heavy rain on the water vapor map, and areas of high wind speed (>20 m/s) on the SST map.

Gridded Binary Data Files

We produce Daily binary data files and Time-Averaged (3-day, weekly and monthly) data files. The daily files consist of AMSR-E geophysical products mapped to a regular grid complete with data gaps between orbits. Two maps exist for each parameter, one of ascending orbit segments (local daytime passes) and the other of descending orbit segments (local nighttime passes). Data on each of the segment maps are overwritten at both the high latitudes where successive orbits cross and at the "seam" or region where the last orbit of the day overlaps the first orbit of the day. Daily data files contain time maps consisting of the UTC observation time for each set of passes (ascending and descending). Time-Averaged data files do not contain any time information.

Each binary data file available from our ftp site consists of twelve (daily) or five (averaged) 0.25 x 0.25 degree grid (1440,720) byte maps. For daily files, six daytime maps in the following order, Time (UTC), Sea Surface Temperature (SST), 10 meter Surface Wind Speed (WSPD), Atmospheric Water Vapor (VAPOR), Cloud Liquid Water (CLOUD), and Rain Rate (RAIN), are followed by six nighttime maps in the same order. Time-Averaged files contain just the geophysical layers in the same order [SST, WSPD, VAPOR, CLOUD, RAIN]. The daily, 3-day and monthly maps are stored in appropriate year and month subdirectories. The weekly data files are stored in the /weeks directory.

The file names have the following naming conventions:

Where "yyyy", "mm", "dd", and "vv" stand for:

The center of the first cell of the 1440 column and 720 row map is at 0.125 E longitude and -89.875 latitude. The center of the second cell is 0.375 E longitude, -89.875 latitude.

The data values fall between 0 and 255. Specific values have been reserved:

The data values between 0 and 250 need to be scaled to obtain meaningful geophysical units. To scale the data, multiply by the scale factors (and add the offsets) listed below:

Read Routines:

Binary file read routines and verification files are available on our ftp server in the amsre/support directory.

Acknowledgement

AMSR-E data are produced by Remote Sensing Systems and sponsored by the NASA Earth Science MEaSUREs DISCOVER Project and the AMSR-E Science Team. Data are available at www.remss.com.

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Last updated: April 28, 2009