The Advanced Very High Resolution Radiometer
(AVHRR):
A Brief Reference Guide

David A. Hastings
National Oceanic and Atmospheric Administration
National Geophysical Data Center
325 Broadway, Boulder, CO 80303

William J. Emery
Department of Aerospace Engineering Sciences
University of Colorado
Campus Box 431, Boulder, CO 80309

Abstract: The Advanced Very High Resolution Radiometer, carried by NOAA's Polar Orbiting Environmental Satellites, has unique characteristics of spectral response, image geometry, frequency of coverage, and accessibility that make it useful for applications in oceanography, terrestrial sciences, and meteorology. We review the history, engineering characteristics, data availability, applications, and future of this sensor. With cited references, this paper constitutes a starting point for more extensive investigations of the data and their applications.

This is the text of a paper that appeared in the journal Photogrammetric Engineering and Remote Sensing (volume 58, no. 8, August 1992, pp. 1183-1188). Although there is a copyright notice on the published paper, the manuscript was prepared by/for an agency of the Government of the USA. It is therefore not subject to copyright.

Table of Contents:

INTRODUCTION

THE ADVANCED VERY HIGH RESOLUTION RADIOMETER (AVHRR), operating on the Polar Orbiting Environmental Satellites (POES) of the National Oceanic and Atmospheric Administration, is the direct descendent of the longest-lived and most influential series of Earth observing satellites ever launched. The current generation AVHRR has evolved into a highly accessible data collection system with a wide range of applications in meteorology, climatology, oceanography, and the study of land surfaces. The impressive growth of applications continues with increasing emphasis on regional and global environmental issues, due to AVHRR's unique position as a provider of daily global coverage of digital imagery from two satellites, truly synoptic views, calibrated thermal data, low cost of direct-readout stations and of data from NOAA.

In this paper, we review the development and implementation of the AVHRR sensor hardware, data collection/processing system and data availability. We also provide an overview of applications and summarize needs and plans for successors to the AVHRR.

HISTORY OF WEATHER SATELLITES

NASA's Television Infrared Observation Satellite (TIROS-1) (Allison and Neil, 1962), launched on 1 April 1960, gave our first systematic images of Earth from space. This single television camera was aligned with the axis of this spin-stabilized satellite which meant that it could point at the Earth only for a limited time each orbit (which naturally collected pictures of North America). This experimental satellite series eventually carried a variety of sensors, evolving as technology and experience increased. Working together, NASA and the Environmental Science Services Administration (ESSA, merged into NOAA at the latter's formation in 1970) stimulated improved designs. TIROS-1 through TIROS-X contained simple television cameras, while four of the ten satellites also included infrared sensors.

One interesting development was the change in location of the camera from the spin axis of the satellite was also turned so that now its side, rather than the central axis, pointed towards the Earth. Called the "wheel" satellite, this new arrangement resulted in the camera collecting a series of circular images of the Earth which, when mosaicked, provided the first global view of the Earth's weather systems from space.

Using this wheel concept, cooperation between NASA and ESSA initiated the TIROS Operational System (TOS) with its first launch in 1966. Odd numbered satellites carried improved vidicon cameras and data storage/replay systems that provided global meteorological data, while even numbered satellites provided direct readout Automatic Picture Transmission (APT) video to low cost VHF receiving stations. APT, now derived from AVHRR imagery, is still provided to thousands of simple stations in schools, on ships, and elsewhere worldwide. Nine wheel satellites, called ESSA-1 through ESSA-9, were launched between 1966 and 1969.

The 1970s saw the Improved TOS (ITOS), which combined APT and global data collection/recording in each satellite. The major improvement was the utilization of guidance systems developed for ballistic missiles that made it possible to stabilize the three axes of the spacecraft. Thus, a single camera could be aimed at the Earth, eliminating the need to assemble a series of circular images to map the world's weather. ITOS also introduced day/night acquisitions and a new series of Scanning Radiometers (SRs), which offered vastly improved data. Later, ITOS carried the Very High Resolution Radiometer (VHRR). As part of international weather data exchange, NOAA introduced the direct reception of VHRR data at no charge to ground stations built by an increasing number of users, beginning in 1972. ITOS-1 and NOAA-1, launched in 1070, were transition satellites of the ITOS series, while NOAA-2 through NOAA-5, launched in 1972-1976, carried the VHRR instrument.

The latest generation of this series has been operational since 1978. TIROS-N (for TIROS- NOAA) and NOAA-7 through the latest NOAA-12 include the Advanced Very High Resolution Radiometer (AVHRR), discussed in the following section. The major advance introduced with this satellite series was the shift from an analog data relay to a fully digital system. Now the data are digitized onboard the spacecraft before being transmitted to the Earth. Also the size and weight of the satellite has changed from under 300 kg with the ESSA series of satellites to over 1200 kg with the TIROS-N satellites. There has been one change in the TIROS-N series and we now have the advanced A-TIROS-N along with the advanced A-AVHRR-2. The primary difference in the AVHRR is the addition of a second thermal infrared band to help in the correction for water vapor attenuation when computing sea surface temperature.
THE AVHRR SENSOR
SENSOR HARDWARE
DATA INGEST, PROCESSING, AND DISTRIBUTION
OPERATIONAL AVHRR DATA PRODUCTS
DIRECT READOUT OF AVHRR DATA
APPLICATIONS OF AVHRR DATA
METEOROLOGY
OCEANOGRAPHY
TERRESTRIAL SCIENCES
SOME EFFECTS OF THE SATELLITE SYSTEM ON APPLICATIONS
THE FUTURE OF THE AVHRR
REFERENCES
APPENDIX
Entire paper (a bit long at 45 kilobytes)
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