Geography Reference
In-Depth Information
is possible that there was a better treatment of the point cloud during data processing
regarding the last return (responsible for DTM generation) in detriment of the data of the
first return (that lead to the DEM generation).
5. 1:25,000 scale
5.1. Cartosat-1: Planialtimetric assessment of orthoimage and DEM
The Cartosat-1 satellite - or IRS P5 - is aimed for cartographic applications, especially
reference applications, for having only a panchromatic band, but with 2 different acquisition
angles in the same passage. Its radiometric resolution is of 10 bits.
The stereoscopic pair analyzed covers the surroundings of São Sebastião, the same area
mentioned before.
The stereoscopic pair, acquired on May 23, 2009, was processed with Orthoengine 10.2, by
PCI Geomatics, using RPCs, with 7 GCPs and 8 Tie Points. The orthoimage was generated
with nominal resolution equal to the rated resolution (2.5 m) and the DEM was resampled
for 10 m. For assessment 30 points were used. All points were surveyed with GNSS
equipment, with relative static positioning, with single frequency trackers.
The results were quite satisfactory, with the orthoimage reaching
a class B for 1:10,000 scale
,
with 93.3% of the points presenting errors of up to 8 m and SD of 2.7 m. Altimetric accuracy
was compatible with the specification for a
class A for 1:25,000 scale
, since 94.1% of the
assessment points presented errors of up to 5 m and SD of 2.8 m.
5.2. ALOS/PRISM: Planialtimetric assessment of orthoimage and DEM
PRISM sensor onboard ALOS
1
satellite acquired data only into panchromatic band, but with
telescopes in three different incidence angles (Backward, Nadir and Forward), with a spatial
resolution of 2.5 m. Operating in this mode, called Triplet, it presented optimal conditions
for DEM generation, considering that different view combinations could be used, according
to relief variation or any other needs.
PRISM data, likewise those from AVNIR2 were distributed by IBGE (
Brazilian Institute for
Geography and Statistics)
to noncommercial users for much lower prices than those practiced
by the market for compatible products. It explains the interest in such data and the need for
assessments.
The results presented here referred to the assessment report of PRISM data in [16] and the
work presented by some IBGE employees in [17], who assessed the accuracy of the
geometry from a PRISM Triplet acquired with a 1B2R processing level covering the
surroundings of the municipality of Itaguaí, in Rio de Janeiro.
The data was processed by Orthoengine 10.1, of PCI, without RPCs, but using 7 GCPs and
11 Tie Points. The orthoimage was generated with a Nadir view of 2.5 m and the DEM was
1
ALOS satellite experienced trouble in April 2011 and was disconnected in May of the same year.
