Download pdf of NOAA/AVHRR chapter from Eurimage Products and Services Guide
The National Oceanographic and Atmospheric Administration (NOAA) has been operating its Advanced TIROS-N (ATN) series of satellites since October 1978. Carrying the Tiros Operational Vertical Sounder (TOVS), a low-data-rate atmospheric sounding package, and the Advanced Very-High Resolution Radiometer (AVHRR), these satellites were designed primarily for meteorological applications, but the AVHRR instrument, in particular, has proved very valuable in a variety of environment-linked earth observation applications.
The TIROS satellites have a circular, polar, sun-synchronous orbit, with an altitude of 840 km and an inclination of 98.7° to 98.9°. NOAA maintains at least two operational satellites in complementary orbits, with the even-numbered satellites crossing the equator at local solar times of approximately 07:30 and 19:30, and the odd-numbered satellites at 02:30 and 14:30.
Thanks to the wide swath of the AVHRR sensor (approximatively 3000 Km), there is a very high revisit interval: 2 passages/day at the equator and circa 4 at mid latitudes.
Eurimage currently provides NOAA/AVHRR images acquired by ESA stations. At present the ESA stations that acquire NOAA/AVHRR data are those of Maspalomas (Canary Isles, Spain), Scanzano (Italy) and Tromsoe (Norway), which give a complete coverage of Europe, North_East Africa and the Middle East.
AVHRR scenes (4 minutes of data), which can cover an area 3000 x 1500 km, are provided in SHARP format. TOVS data (the low-data-rate atmospheric sounding package on the NOAA satellite) is also provided, for the entire pass, with each AVHRR scene. Auxiliary information, such as ground reference points, orbit and attitude data, calibration coefficients and geographical information (coastline, state boundaries and/or latitude longitude grid flags), are also provided with the image data.
All AVHRR products are system corrected but not geocoded.
SHARP (Standard-family HRPT Archive Request Product) is the ESA-Earthnet format for AVHRR and TOVS data. It adopts the internationally-recognised Standard-Family Tape Format as defined by the Landsat Technical Working Group (LTWG).
AVHRR scenes (4 minutes of data) are provided on Exabyte cassette. You can order up to 40 scenes on an Exabyte tape - full details are given in the Eurimage Price List.
Image navigation (location) is carried out during Level 1 data generation, using the orbital model for the satellite location and is tested by an operator who carries out further correction if necessary.
SHARP-2 products are in the original spacecraft projection. A location grid of tie points (lat/long) is given in the suffix data (every 16th image file record).
SHARP-1 is the implementation of the superstructure concept of the High-Resolution Picture Transmission (HRPT). It contains the raw digital data with supplementary information such as: latitude/longitude grid, coastlines, state boundaries.
SHARP-2 products are produced from archived SHARP-1 day-time data.
SHARP-2 products are not archived. TOVS data remains the same as for SHARP-1 products.
Each pixel contains image data (calibrated), classification and geographical information (boundaries, coastlines and lat/long grid flags). Each pixel consists of 2 bytes; 10 bits are used for image data, 3 bits for the classification and 3 bits for geographical data, iNcluding land, cloud, sea, snow/ice and unclassified pixels.
The SHARP level-2A (Calibrated Product) contains calibrated data from the AVHRR channels (i.e. level 1 data calibrated and converted to measurements of Equivalent Reflectance, Spectral Radiance and Brightness Temperature) and a classification of the image.
For the Level 2A product, Level 1 raw data is calibrated and classified. The visible channels (1 and 2) are converted from raw data to Equivalent Reflectance, while channels 4 and 5 (infrared) are converted to Brightness Temperature, corrected by non-linear effects, and the third infrared channel (3) is converted to Spectral Radiance.
This product can be produced with data from all the operating NOAA satellites; however, if the data is derived from the even-numbered satellites, band 5 is empty.
Level 2A Product Image Data:
Band refers to the output data structure of the SHARP products
Channel refers to the input satellite data acquired in different wavelengths.
|
Band |
Content |
|
1 |
Channel 1 Equivalent Reflectance |
|
2 |
Channel 2 Equivalent Reflectance |
|
3 |
Channel 3 Spectral Radiance |
|
4 |
Channel 4 Brightness Temperature |
|
5 |
Channel 5 Brightness Temperature |
The SHARP level-2B (Geophysical Product) contains geophysical parameters extracted from AVHRR raw data (Vegetation Index and Sea Surface Temperature) as well as calibrated data and a classification of the image.
Two bands of the Level 2B product contain class-dependant geophysical parameters: Vegetation Index (NDVI) over land, and Sea Surface Temperature (SST) over sea. The other three bands consist of calibrated data similar to that in the Level 2A product.
This product cannot be produced with data from the AVHRR/1 instrument.
Level 2B Product Image Data:
Band refers to the output data structure of the SHARP products
Channel refers to the input satellite data acquired in different wavelengths.
|
Band |
Content |
Description |
|
1 |
Over Land |
Normalised Difference Vegetation Index (NDVI) |
|
1 |
Over Other Areas |
Equivalent Reflectance From Channel 1 |
|
2 |
Channel 2 |
Equivalent Reflectance |
|
3 |
Channel 3 |
Spectral Radiance |
|
4 |
Channel 4 |
Brightness Temperature |
|
5 |
Over sea |
Sea Surface Temperature (SST) |
|
5 |
Over Other Areas |
Brightness Temperature From Channel 5 |
- the red spots are fires burning in the forest
