Full text: XVIIIth Congress (Part B4)

  
geocoded satellite images to rectify several hundred aerial 
photographs; 2) establish efficient photo-interpretation and 
feature encoding procedures compatible with a vegetation 
classification system that takes into account vegetation species, 
human impacts and hurricane damage; and 3) integrate GPS 
surveys with attribute recording and digital image processing 
on a laptop computer to facilitate the real time collection of 
ground truth information by helicopter surveys. 
2.1 South Florida GPS Surveys and Satellite Image Mosaic 
To ensure the registration of vegetation, transportation and 
hydrographic features in a GIS database, it was first necessary 
to establish a network of ground control points (GCPs) 
adequate for rectifying eight SPOT panchromatic images (10-m 
resolution) of the study area. Past experience has shown that 
because of their excellent internal geometry, only 4 to 6 GCPs 
per image are required to geocode a SPOT satellite image to a 
planimetric accuracy of + 0.5 to + 1.0 pixel - or + 5 to + 10 m 
on the ground. Such accuracies are compatible with U.S. 
National Map Accuracy Standards for 1:24,000 scale maps and 
were considered acceptable for densifying the horizontal 
control points needed to rectify the aerial photographs from 
which the database would be constructed. 
The survey to establish GCPs was influenced by the existing 
road network and by the availability of 1:24,000 scale 
topographic line maps of recent vintage for the lands adjoining 
the Parks. Thus, it was decided to use the existing maps for 
perimeter control and to conduct the GPS survey along the few 
roads through the middle of the study area to provide the 
interior control necessary to rectify the satellite images. 
Control points included the intersections of roads and of roads 
and canals, both of which are easily located on the SPOT 10-m 
panchromatic images. In addition, the survey included eight 
monumented National Geodetic Survey (NGS) and Florida 
GPS (FLGPS) base points of Order B (1:1,000,000) accuracy 
(or better) which were used to adjust the network. Based on 
checks conducted in the post-processing adjustment of the GPS 
observations, the accuracy to which the UTM coordinates of 
the 23 points were established as referenced to NAD 83 was 
about + 0.05 m (RMSE,y). 
The SPOT image mosaic was created from individual SPOT 
scenes using the Desktop Mapping System (DMS)'M software 
package. Each digital SPOT image (or tile) was rectified to the 
UTM coordinate system using 6 to 15 GCPs per image and 
then placed at its correct location (according to the UTM 
coordinates of the upper left corner pixel) within a coordinate 
box for the entire study area. In order to facilitate its use, a 
UTM grid (NAD 83) with 5,000 m spacing was registered to 
the mosaic. The planimetric accuracy of the geocoded mosaic 
was evaluated at 29 withheld control points (check points) and 
found to be better than + 1.5 pixels. The mosaic occupies 
slightly more than 200 Mbytes of disk space. 
2.2 Interpretation of CIR Aerial Photographs 
Development of an accurate, detailed vegetation database for 
the Parks requires the use of remotely sensed data of sufficient 
resolution to allow the identification of plant species/asso- 
932 
ciations, the delineation of one-hectare or larger vegetation 
plots and classification accuracies of 90 percent of better. 
These requirements precluded the use of Landsat TM (28.5 m) 
or SPOT (20 m) multispectral imagery for the construction of 
the vegetation database. Instead, the use of aerial photographs 
was deemed essential for the project. Color infrared (CIR) 
aerial photographs of 1:40,000 scale acquired as part of the 
U.S. Geological Survey (USGS) National Aerial Photography 
Program (NAPP) in 1994 and 1995 were purchased for the 
entire South Florida study area. In order to facilitate the 
interpretation of these photographs and the construction of 
vegetation coverages in digital format, vegetation classes were 
delineated directly on CIR paper print enlargements (4x) 
produced from the CIR film transparencies. Point features 
common to both the SPOT images and the analog air photo 
enlargements were annotated, numbered and their UTM 
coordinates determined from the geocoded SPOT images to 
establish a GCP file for each CIR photograph. 
The GCPs transferred to the photographs were then digitized, 
along with the vegetation polygons and other point and line 
features. By digitizing the GCPs first, a set of photo recti- 
fication coefficients were generated that allowed x,y digitizer 
coordinates for the vegetation polygons to be transformed to 
UTM map coordinates (Easting, Northing). This procedure 
permitted a segregation of tasks (interpretation, digitizing, 
editing) and greatly facilitated the development of the veg- 
etation database. To further improve digitizing efficiency in 
areas of complex vegetation patterns, clear plastic overlays with 
annotated vegetation boundaries were scanned at 65 um and 
accessed by the VTRAK® software package (Laser-Scan, Inc.) 
for automatic vectorization and input to ARC/INFO®. Tests 
conducted to assess the accuracy to which the features were 
digitized yielded RMSE,, values of between + 5 and + 10 m. 
2.3 Field Verification with GPS Assisted Helicopter Surveys 
and Vegetation Classification 
A new Everglades Vegetation Classification System was 
developed in conjunction with personnel from both the NPS 
and South Florida Water Management District (SFWMD) 
because existing vegetation classification schemes did not 
contain the level of detail required for this vegetation mapping 
project. This classification system includes hierarchical veg- 
etation classes at the individual species or species association 
level that can be identified from the CIR aerial photographs. In 
addition to the floristic characterization of the naturally 
occurring Everglades plant communities, the classification 
system includes categories of human impacts and episodic 
disturbances that influence vegetation species distributions. 
For example, invasive exotic plants, indicators of human 
influence such as agriculture or off-road vehicle (ORV) trails 
and three hurricane damage classes are added as modifiers to 
the vegetation class. 
Fieldwork to verify the image interpretation was greatly 
facilitated by the use of NPS Bell Jet Ranger 206 helicopters 
that are available for ground truth collection. Since helicopter 
flight time is expensive (— $ 650.00/hr), a procedure involving 
use of the SPOT image mosaic and the latest technology in 
laptop computers, GPS receivers and image processing/posi- 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
	        
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