SMEX02 QuikSCAT/SeaWinds Backscatter Data, Iowa

Summary

This data set includes data collected over the Soil Moisture Experiment 2002 (SMEX02) area of Iowa, USA, during June and August, 2002. The SeaWinds scatterometer on NASA's QuikScat satellite collected backscatter data. Data are provided in binary arrays, digital images, and video (.avi) files, and are available via FTP.

These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

Citing These Data

Nghiem, S. 2004. SMEX02 QuikSCAT/SeaWinds Backscatter Data, Iowa. Boulder, CO, USA: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	Binary, browse image, and video files
Spatial coverage and resolution	39° to 45°N, -98° to -89°W 25 km resolution
Temporal coverage and resolution	Daily coverage 1 June through 21 August 2002
File naming convention	Binary data files are named using the following format: Year, month, day, polarization (H or V), version, ascending or descending.bin For example: 20020828Hc5des.bin See below for details and other data file naming conventions
File size	Binary files are 6 KB browse image files are 24.8-57.2 KB video files are 68.9-74.6 MB
Parameter(s)	Backscatter
Procedures for obtaining data	Data are available via FTP.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Son V. Nghiem
Jet Propulsion Laboratory
California Institute of Technology

Technical Contact

2. Detailed Data Description

Format

Data are binary arrays, browse image files, and video files.

• Binary - binary files are stored as 4 byte, big-endian, floating point (real) values. Data are 46 column x 31 (row) arrays in row major order on a .2 degree grid.
• Image - image files are in .GIF format, and include four browse images per day
• Video - video files are in .AVI format, and are compilations of the daily images

File and Directory Structure

The following table shows the directories and contents of the directories.

Directory/Subdirectory	Files
data	All binary data files
images/polarization and direction directories	Four browse images per day, with names that indicate polarization and direction
movies	AVI movies made from the images in the images directory
reader	Fortran reader to read data files

File Naming Convention

Binary Files

The fields in the binary file names are as follows:

• YYYY - four-digit year
• MM - two-digit month
• DD - two-digit day
• H or V - horizontal or vertical polarization
• c5 - indicates that the data are gridded at 1/5 of a degree in latitude and longitude, derived from cell sigma0 data (rather than slice sigma0 data).
• asc or des - ascending or descending
• bin - the file extension, indicating binary format

For example, the data in the file "20020828Hc5des.bin" were obtained 28 August 2002 at a horizontal polarization and a descending pass.

Image Files

The browse image files have a complex naming convention, explained by the following table. The field descriptions use examples from the file "20020609_1602Hc5des.gif."

• YYYY MM DD - the date in yar, month, day format
• Number of revisions (16) - is the number of revisions from which any data are included
• Check (02) - an internal check.
• The fourth field (Hc5des) has several components:
  • H - data are from the inner beam (H polarization).
    V - indicates that data are from the outer beam (V polarization)
  • c5 indicates that the data gridded at 1/5 of a degree in latitude and longitude, and derived from cell sigma0 data (rather than slice sigma0 data).
  • asc - indicates an ascending pass.
    des - indicates a descending pass
• Extension (gif) - indicates the image format

Video Files

The video files follow this convention:

• qscat - indicates the file is from QuikSCAT
• v_pol or h_pol - vertical or horizontal polarization
• ascending or descending
• extension - identifies the file as .avi format

For example, "qscat_v_pol_ascending.avi."

File Size

Each binary data file is 6 KB, image files are 24.8-57.2 KB, and video files are 68.9-74.6 MB.

Spatial Coverage

Southernmost Latitude: 39° N
Northernmost Latitude: 45° N
Westernmost Longitude: -98° W
Easternmost Longitude: -89° W

Spatial Resolution

Measurements are in 25 km resolution.

Grid Description

Data are gridded in 0.2 degrees in latitude/longitude projection.

Temporal Coverage

Data cover the period of 1 June through 21 August 2002.

Temporal Resolution

Daily coverage includes four browse images per day. Images include ascending and descending images for both horizontal (H) and vertical (V) polarizations.

Parameter or Variable

Parameter Description

The parameter for this data set is microwave backscatter. The following chart shows the backscatter data for the SMEX02 study period. (Click on the image to see a larger version of the chart.)

Unit of Measurement

Backscatter measurements are given in decibels (dB).

Sample Data Record

The following image is a portion of the binary data file "20020831_Vc5des.bin."

The next image is a small version of the image file "20020827_1502Vc5des.gif."

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

Total volume of the binary, image, and movie files is 603.63 MB.

Software and Tools

A Fortran reader is available for download with the binary data files. The Fortran code was written in Fortran77 and tested using a Sun compiler. You can also view the data with other appropriate applications.

Related Data Collections

See Soil Moisture Experiment (SMEX) for more information.

4. Data Acquisition and Processing

Sensor or Instrument Description

The QuikSCAT satellite was successfully launched at 7:15 p.m. Pacific Daylight Time on 19 June 1999 from the Vandenberg Air Force Base in California. The satellite carries the SeaWinds scatterometer for ocean wind measurements. SeaWinds uses a rotating dish antenna with two spot beams that sweep in a circular pattern. The antenna radiates microwave pulses at a frequency of 13.4 GHz across broad regions on Earth's surface. The scatterometer collects data at 13.4 GHz on both ocean and land. Backscatter data, at a radiometric resolution of 7 km x 25 km, are acquired with the vertical polarization at a constant incidence angle of 54° over a conical-scanning swath of 1800 km, and with the horizontal polarization at 46° over a 1400-km swath. The large swath can cover almost the entire globe in two days even at low latitudes and equatorial regions.

Processing Steps

The cell sigma0 data were grouped by day, local time of day, beam, and geographic location. Data quality flags were checked. Only data passing the quality check were used. The average sigma0 was calculated for each group using natural numbers, not dB.

5. References and Related Publications

S. V. Nghiem and G. Neumann. 2004. "QuikSCAT/SeaWinds Data Package for SMEX 2002." JPL CL 04-0432, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California.

SeaWinds at JPL

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

AMSR-E	Advanced Microwave Scanning Radiometer - Earth Observing System
AVI	Audio-Visual Interleave (video format)
FTP	File Transfer Protocol
GIF	Graphics Interchange Format
JPL	Jet Propulsion Laboratory
SMEX	Soil Moisture Experiment

Document Creation Date

May 2004

Document URL

http://nsidc.org/data/docs/daac/nsidc0233_smex_quikscat.gd.html