ALN No. 53: Orr et al.: Sidebar 2: Advanced Very High Resolution Radiometer (AVHRR)

Orr et al.: Sidebar 2: Advanced Very High Resolution Radiometer (AVHRR)

AVHRR was first launched in 1978 on the TIROS-N satellite, one of NOAA's Polar Orbiting Environmental Satellites (POESs) with daily global coverage. The AVHRR sensor instrument has since been aboard NOAA satellites NOAA-6,7,8,9,11, and 14, and is now aboard NOAA-16.

AVHRR circles the globe twice a day from an altitude of 833 km. The images cover a 4,600 km × 2,900 km area, and have a 1.1 km spatial resolution. This sensor collects data from 0.58 µm to 12.50 µm, which is divided into 5 spectral bands or channels (range of wavelengths). The two bands important to vegetation mapping are 1 and 2.

These bands are used to calculate the Normalized Difference Vegetation Index (NDVI) with values that normally range between 0.1 and 0.6. Snow, clouds, and water have such a high reflectance in band 1 that they give negative NDVI values, whereas bare soil and rocks have such similar reflectances in the two bands that they yield values near 0.

Wavelength Range (µm)
Band Number	NOAA 6, 8, 10 (a)	NOAA 7, 9, 11, 14, 16 (a)	Primary uses
1	0.58-0.68 (red)	058-0.68 (red)	Daytime cloud and surface mapping, snow and ice extent.
2	0.725-1.10 (near IR)	0.725-1.10 (near IR)	Surface water delineation, snow and ice extent.
3	3.55-3.93	3.55-3.93	Detecting hot targets, nighttime cloud mapping.
4	10.50-11.50	10.30-11.30	Determining cloud and surface temperatures, day or night cloud mapping.
5	None	11.50-12.50	Determining cloud and surface temperatures, day or night cloud mapping, water vapor correction.
(a) Even-numbered satellites cross the equater at 7:30 AM and 7:30 PM; odd-numbered satellites cross the equator at 2:30 AM and 2:30 PM.

Source: Avery, T.E. and G.L. Berlin. 1992. Fundamentals of remote sensing and airphoto interpretation, 5th ed. Upper Saddle River, N.J.: Prentice-Hall.

The vegetation index used by RangeView is derived from AVHRR spectral data by the USGS Earth Resources Observation Systems (EROS) Data Center in Sioux Falls, South Dakota. Their NDVI product is regularly used by researchers and is available by subscription, with updates generally available within 10 days of satellite data acquisition. The data set extends back to 1989 and is based on a temporal maximum value composite period of 14 days to try and limit the impact of clouds on the vegetation signal. The geographic coverage includes the conterminous U.S., southern Canada, and northern Mexico. RangeView produces additional products from the NDVI data including difference from average, difference from previous period, and difference from previous year.

(adapted from the RangeView Glossary: http://rangeview.arizona.edu/glossary/glossary.html)

AVHRR NDVI data may be ordered through the EROS Data Center:
http://edcwww.cr.usgs.gov/products/landcover/ndvi.html

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