Radio-metrically and geometrically corrected Landsat Thematic Mapper
(TM) Level 1G images (GLCF) covering the study area (path/row
158/68 - 158/77) were used to identify areas of potential littoral
forest along the entire eastern coast of Madagascar. Images were
downloaded from the Global Land Cover Facility website
http://glcfapp.umiacs.umd.edu:8080/esdi/index.jsp
We examined five images dated from 1999 - 2000 and classified all areas
within 5 km of the coastline as forest or non-forest. Littoral forest in
eastern Madagascar occurs on sandy soil close to the coastline, while forest
further inland is more commonly characterized by laterite soils. ArcView
Image Analyst was used to import, view, and analyze all Landsat and aerial
photographs. Image bands 5, 4, and 3 were assigned red, green, and blue
respectively. Using our techniques and the 30 m resolution of the Landsat
images, it was not possible to distinguish primary from secondary forest.
Images were compared to known littoral sites on Du Puy and Moat’s (1996) map
of estimated primary vegetation in Madagascar, along with ground truth data
and field knowledge of areas recently visited by two of the authors. The
characteristics of these areas were then used to identify other spectrally
similar areas, resulting in six sites of priority for aerial photography
and fieldwork.
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1A Lake Sahaka, north of
Vohemar 13° 4’S, 49° 54’E 1B
Manakana Forest, south of
Vohemar 13° 42’S, 50° ’E
2A Tanambao-Ambodimanga
Forest, north of Soanierana-Ivongo 16° 45’S, 49° 42’E
2B Ambohidena Forest,
northeast coast of Ile Sainte Marie 16° 51’S, 49° 57’E
3 Vohibola Forest, near Brickaville 18° 34’S, 48° 29’E
North,
South
4A Nankinana Forest, north of Nosy Varika 20° 16’S, 48° 7’E
4B Ambahy Forest, south
of Nosy Varika 20° 5’S, 48° 30’E
5 Mahabo Forest, south
of Farafangana 23° 11’S, 47° 42’E
6 Fort Dauphin Forests,
Ste. Luce, Mandena, Petriky 24° 57’S, 47° 00’E
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Aerial photographs for the eastern coast of Madagascar were obtained
during May 2003 using a Nikon D1x digital camera attached to the belly
of a low flying Cessna aircraft. In order to capture latitude/longitude
data for each image, a Magellan GPS unit was attached to the Nikon camera,
which was in turn attached to a laptop, and images were taken via remote
control using Nikon Capture 2 software.
The data captured with each image included a latitude and longitude
at the center of the photo. Latitude and longitude control points for
the upper left and lower right of each image were estimated using the
length and height in kilometers for that image. The resulting three
control points and the more recent Landsat images were then used to
geo-rectify the aerial photos using ArcView Image Analyst. Area for
each image was calculated in hectares using the Image Analyst seed tool
to create polygons for all forested areas. Based on the preliminary
Landsat analyses we selected seven priority sites to investigate using
our aerial photographs.
Finally, ortho-rectified Landsat TM images were used to estimate
the extent of forest prior to 1995 for each of the seven sites
selected in this study. Landsat images were chosen on the basis of
the lowest percent of cloud cover and then oldest date possible between
the years 1989 -1994. A total of 9 images dated 1989-1994 were used to
classify areas within 5 km of the eastern coastline into forest and
non-forest categories and forested area calculated in hectares. Change
in forest cover for each of the seven sites in our study was then
determined by comparing the area of forest present in these images to
those of the recent aerial photographs.
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