The dates for which satellite imagery was avail-
Sciences Remote Sensing Laboratory at Dartmouth
able were limited by the repeat cycle of each sen-
College, Hanover, New Hampshire, and the De-
sor and the weather. The Landsat Thematic Map-
partment of Energy Pacific Northwest Laboratory,
per (TM) acquires 8-bit data in seven wavelength
Richland, Washington. The 16-bit data were res-
bands--three visible (blue, green and red), one
caled to 8-bit and rectified to the UTM projection
zone 15 based on NAD27 using 30- 30-m pixels.
near-infrared, two mid-infrared and one thermal
infrared band. The near-polar, sun-synchronous
The images were rectified approximately to Na-
orbit of Landsat allows the satellite to image the
tional Map Accuracy Standards for maps of scale
same area of the earth every 16 days. The TM data
1:20,000 or smaller (USGS 1989). The horizontal ac-
are collected using a 30-m instantaneous-field-of-
curacy standard states that for maps on publica-
view (IFOV) for all bands except the thermal
tion scales of 1:20,000 or smaller, no more than 10%
band, which has a 120-m IFOV. The swath width
of the points tested shall be in error by more than
of the sensor is 185 km. The scenes were pur-
1/50th of an inch (0.05 cm) from their intended
chased from the Earth Observation Satellite Com-
location. The rectified data were not exhaustively
pany (EOSAT, Lanham, Maryland) and were geo-
evaluated, but the majority of the points met this
metrically corrected and rectified to the UTM pro-
standard.
jection based on the NAD27 datum, using 25-
The Erdas/PC version 7.4 (Erdas, Inc., Atlanta,
25-m pixels.
Georgia) DIGSCRN module was used for "heads-
The Systme Probatoire d'Observation de la
up" digitizing of the flood vectors from the recti-
Terre (SPOT) (SPOT Image Corporation, Reston,
fied images. This module allows digitizing of vec-
Virginia) satellite images are acquired in a 10-m
tor data against an image backdrop that is dis-
resolution panchromatic mode over the spectral
played on the computer screen in either the Erdas
range of 0.51 to 0.73 m. The orbit pattern for
.LAN or .GIS format. For the TM data, band 4
(0.760.90 m) was used for delineation of the
SPOT-1 repeats every 26 days. However, the
pointable optics of the SPOT enable off-nadir
flood vectors. The near-IR wavelengths of band 4
viewing during satellite passes separated alterna-
provide a sharper contrast between the vegetation
tively by 1 and 4 days (and occasionally 5), de-
and the water than the other bands.
pending on the latitude of the area viewed. This
The digitized vector data were output to a file in
revisit capability is important because it increases
a .DIG format. A UNIX awk script was used to
the potential frequency of coverage, enabling
convert the .DIG file into a format ready to import
viewing of a given area at frequencies ranging
into ARC/INFO using the GENERATE command
from successive days to a few weeks. The swath
(Appendix A). The TM and ERS-1 data were pro-
width of the sensor is 60 km. The 8-bit panchro-
jected to the correct UTM zone based on NAD83.
matic data were radiometrically and geometrical-
The datum of the SPOT data was WGS84, which
ly corrected and rectified to zone 15 of the UTM
was assumed to be identical to NAD83.
projection based on the WGS84 datum with 10-
10-m pixels.
APPLICATION OF SPATIAL DATABASE
Microwaves are capable of penetrating the at-
mosphere under virtually all conditions. Since
In support of emergency management opera-
cloudiness was a continuing problem in portions
tions being conducted by the Readiness Branch, a
series of 8.5- 11-in. (22- 28-cm) maps was pro-
of the Upper Midwest as floods were cresting, the
majority of the imagery acquired for the emergen-
duced by the RSGISC for each of the seven reaches
of river. The maps covered 20,000- 20,000-m re-
cy came from the European Remote Sensing Satel-
lite Synthetic Aperture Radar, ERS-1 SAR (Radar-
gions and included roads, railways, hydrography,
sat International, Richmond, British Columbia).
county boundaries and, when available, inunda-
The ERS-1 operates a SAR instrument at the C-
tion data.
band frequency (λ = 5.7 cm) with VV-polarization,
The 8.5- 11-in. format was chosen as a result of
a 100-km swath width and a spatial resolution of
previous experience gained by the RSGISC
better than 30 m, thus allowing the sensor to "see"
through participation in the recovery from Hurri-
through the clouds that are present during peri-
cane Andrew and the Federal Emergency Manage-
ods of precipitation.
ment Agency's (FEMA) earthquake preparedness
The 16-bit ERS-1 SAR images were obtained
exercise, Response '93 (FEMA 1993). These experi-
geometrically corrected but not rectified. Rectifica-
ences showed that by producing the maps in an
tion was done by the Department of Geological
Encapsulated PostScript (EPS) format they can be
6
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