Daily Global Area Coverage (GAC) Images for Africa from the NOAA AVHRR Radiometers, 1982-1992, from SAI/JRCEntry ID: SAI_JRC-AVHRR_GAC_AFRICA_LAND
Abstract: General information about NOAA-AVHRR can be queried by interested
users in the category 'Sensor' and 'Source'. Some basic information is
The Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA 6,
8, 10 and TIROS-N measured in four spectral bands, while the NOAA 7, 9
and 11 are measured in 5 bands. The primary objective of the AVHRR
... instrument is to provide cloud top and sea surface temperatures
through passively measured visible, near infra-red and infra-red
spectral radiation bands. Nevertheless these data are widely used for
terrestrial applications, such as land cover mapping and vegetation
The available data provide a long term AVHRR Global Area Coverage
(GAC) data set with particular emphasis placed on the continent of
Africa. Normalized Difference Vegetation Index (NDVI), channel 2
reflectance, channel 3 and 4 brightness temperatures, an approximate
surface temperature and a cloud probability image are available on a
daily basis from January 1982 to December 1992 for the whole African
Continent at a resolution of 5 km.
The remaining data from the entire GAC time series (July 1981 to the
present) will be processed by the end of 1995.
Channels 1 and 2 are converted to radiance using the August desert
calibration coefficients published by Holben et al. (1990).
Radiances in channels 1 and 2 are converted to 'top of atmosphere'
reflectances (ToA). Brightness temperatures are calculated for
channels 3, 4 and 5 using the inverse Planck function (Kidwell 1991).
Channels 4 and 5 are corrected for non-linearity of sensor response to
give true brightness temperatures using pre-launch correction
coefficients (Planet 1988). The brightness temperature and
reflectance images are scaled to 8 bit integers.
The ToA reflectances and brightness temperatures are used to identify
cloudy pixels. The channel 1 and 2 reflectances are then used to
compute the NDVI, and channels 4 and 5 true brightness temperatures
used to compute an approximate surface temperature using a 'split
window' technique (Price 1984). This does not take variations in
emissivity into account, and so is only of limited accuracy.
The NDVI, channel 2 reflectance, channels 3 and 4 brightness
temperature, surface temperature and the cloud probability channel are
then geometrically corrected. Geometric correction involves three
steps; navigation using the ELPs from the raw data, correlation with a
reference image data base to provide ground control points for fine
correction, and resampling into a daily continental scale mosaic.
For Africa a Mercator map projection is used. The Africa GAC mosaic
map center coordinates are 0#161#, 17.25#161# E, pixel size at the
equator is 5 by 5 km, giving an image of 1800 lines by 1600 columns,
with top left co-ordinates 37.59#161# N, 18.64#161# W, bottom right
37.59#161# S, 53.64#161# E. As a function of the Mercator projection
the resolution degrades by approximately 20% at the northern and
southern limits; for example the ground area represented by each pixel
is 30 km2 at 35#161# N or S, (4 km, x axis by 7.5 km, y axis) compared
with 25 km2 at the equator.
The processed data sets are stored as ERDAS 7.4 format files on a
gigatek optical disk juke box. Data are currently made available
through formal collaborative research agreements between outside
laboratories and the Joint Research Centre. In such instances data
costs are for marginal cost of reproduction only.
These data will become available to the international research
community through the EC and European Space Agency initiative, the
Centre for Earth Observation (CEO).
The data sets have already provided new information concerning inter
and intra annual variations in vegetation fire dynamics for Africa and
have been used to derive forest seasonality information through the
JRC`s thematic projects such as TRopical Ecosystem and Environment
observations by Satellite (TREES).
See separate entry for TREES.
Example data can be found on the CEO World Wide Web home page:
(Click for Interactive Map)
Start Date: 1982-01-01Stop Date: 1992-12-31
ATMOSPHERE > ATMOSPHERIC TEMPERATURE > SURFACE AIR TEMPERATURE
ATMOSPHERE > CLOUDS > CLOUD PROPERTIES > CLOUD FREQUENCY
ATMOSPHERE > ATMOSPHERIC RADIATION > REFLECTANCE
BIOSPHERE > VEGETATION > VEGETATION COVER > NDVI
BIOSPHERE > VEGETATION > VEGETATION INDEX
HUMAN DIMENSIONS > ENVIRONMENTAL IMPACTS > BIOMASS BURNING
HUMAN DIMENSIONS > HABITAT CONVERSION/FRAGMENTATION > DEFORESTATION > REGIONAL DEFORESTATION
LAND SURFACE > SOILS > SOIL TEMPERATURE
LAND SURFACE > SURFACE RADIATIVE PROPERTIES > REFLECTANCE
SPECTRAL/ENGINEERING > INFRARED WAVELENGTHS > BRIGHTNESS TEMPERATURE
SPECTRAL/ENGINEERING > INFRARED WAVELENGTHS > INFRARED FLUX
SPECTRAL/ENGINEERING > INFRARED WAVELENGTHS > INFRARED IMAGERY
SPECTRAL/ENGINEERING > INFRARED WAVELENGTHS > REFLECTED INFRARED
SPECTRAL/ENGINEERING > INFRARED WAVELENGTHS > SENSOR COUNTS
SPECTRAL/ENGINEERING > VISIBLE WAVELENGTHS > SENSOR COUNTS
SPECTRAL/ENGINEERING > VISIBLE WAVELENGTHS > VISIBLE FLUX
SPECTRAL/ENGINEERING > VISIBLE WAVELENGTHS > VISIBLE IMAGERY
BIOSPHERE > ECOLOGICAL DYNAMICS > FIRE ECOLOGY > FIRE OCCURRENCE
ISO Topic Category
Quality This was a feasibility study to test the potential recovery of palynomorphs in
the area of interest for the SHALDRIL project.
For this project, piston core samples were evaluated. The recovery exceeded
our expectations and a diverse palynomorph assemblage was recovered (diverse
both in age and in term of environmental significance).
Access Constraints The staff at the Antarctic Research Facility in Florida was extremely helpful
and provided all data on time.
Use Constraints All data are currently being published and will be accessible broadly soon.
Data Set Progress
Email: swarny at lsu.edu
Louisiana Museum of Natural Science 119 Foster Hall
City: Baton Rouge
Province or State: LA
Postal Code: 70803
Warny, S. Anderson, J.B., ,Londeix, L., and Bart, P.J., submitted. Analysis of
the dinoflagellate cyst genus Impletosphaeridium as a marker of sea-ice
conditions off Seymour Island. In Antarctica: A Keystone in a Changing World
Online Proceedings of the 10th ISAES, edited by A.K. Cooper and C.R. Raymond et
al., USGS Open-File Report 2007-xxx, yyy, 1-4, doi: 10.3133zzzzz.
Warny, S., to be submitted in March. Palaeostomocystis spp.: A potential
indicator of neritic subpolar environments from Masstrichtian to Pleistocene.
Palynology special volume dedicated to John Wrenn.
Bart, P.J., Ehrmann, W.U., Hillenbrand, C.D., Iwai, M., Winter, D., and Warny,
S., 2006. Are Antarctic Peninsula Ice Sheet grounding events manifest in
sedimentary cycles on the adjacent continental rise? Marine Geology. In press.
Warny, S., Wrenn, J.H., Bart, P.J., Askin, R.E., 2006. Palynological analysis
of the NBP03-01A transect in Northern Basin, western Ross Sea, Antarctica: a
Late Pliocene record. Palynology, 30: 151-182,
Tedford, R. and Warny, S., 2006. Investigating the cake-layer Earth and its
fossil record. National Science Teacher Association, December, p. 40-44.
Fauquette, S., Suc, J.-P., Bertini, A., Popescu, S.-M., L., Warny, S., Bachiri
Taoufiq, N., Perez Villa, M.-J., Ferrier, J., Chikhi, H., Subally D. and
Clauzon, G., 2006. How much the climate forced the Messinian Salinity Crisis?
Quantified climatic conditions from pollen records in the western Mediterranean
region. Palaeogeography, Palaeoclimatology and Palaeoecology, 238: 281-301.
Egger, A., Eriksson, S., Franks S., Hall, M., Marlino, M., Mogk, D. Ruzek, M.,
Scotchmoor, J., and Warny, S., 2006. Geoscience Education and Public Outreach
Network (GEPON). Report of a workshop held at UNAVCO, Boulder, Colorado, March
22-24, 2006. Marlino, M. and Scotchmoor, J. (eds). Available online at:
Warny, S., Bart, P.J. and Suc, J.-P., 2006. Glacioeustatic, climatic, and
tectonic influences on the Messinian Salinity Crisis. Abstract, SEAL
conference, Aix, France, 24-29 September.
Bart, P.J., Egan, D., and Warny, S., 2005. Late-Miocene/early-Pliocene
transition from temperate to sub-polar climatic conditions on the Pacific
margin of the Antarctic Peninsula outer continental shelf. JGR-Earth Surface.
Bart, P.J., and Warny, S., 2005. Antarctic Peninsula Ice Sheet grounding
events on the Pacific-margin continental shelf during the late Miocene/early
Pliocene compared to two drift-derived proxies on the adjacent continental
rise. Abstract, AGU (American Geosciences Union), New Orleans, Louisiana,
Bart, P.J., Warny, S., and Egan, D., 2005. Dynamics, nature and timing of
Antarctic Peninsula Ice Sheet grounding events on the Pacific margin outer
continental shelf during the late Miocene/early Pliocene. Abstract, EGU
(European Geosciences Union), General Assembly, Vienna, Austria, 24 - 29 April
Creation and Review Dates
DIF Creation Date: 2007-03-08
Last DIF Revision Date: 2010-07-02