Geography Reference
In-Depth Information
With ENVI / ASTER MDT: using the same scenes (same date), with the same processing
level and control points; and using the same scene, however with L1B processing level
and without control points.
The orthoimages and DEMs generated for assessment had the same resolution as raw data:
15 m, despite having carried out tests of the DEM with pixels resampled up to 60 m,
without perceiving significant difference.
There was no disagreement between the results obtained for planimetry, placing the VNIR
orthoimages in
class A for 1:50,000 scale
, with 92.7% of the 41 assessment points presenting
errors of up to 40 m, with a standard deviation of 11.6 m.
In the case of altimetry, however, results were different depending on the approach used in
DEM generation. Using Orthoengine, the worst results were obtained, since DEM meets the
specifications for
class A for 1:100,00 scale
, with 94.2% of the assessment points presenting
errors of up to 25 m, with a standard deviation of 10.5 m. When using the
ENVI
/ASTERDTM,
with the same scenes, processing level and same 12 control points, the result
changes to a
class C for 1:50,000 scale
, with 92.7% of the assessment points presenting errors
of up to 15 m, with standard deviation of 8.6 m. Using the scenes with processing level L1B
with
ENVI /ASTERDTM,
without any ground control point, the specification for a
class C
for 1:50,000
scale
is reached, with 96.3% of the 41 assessment points presenting errors of up
to 15 m, with a standard deviation of 6.1 m.
These results ensued a questioning to the PCI representative in Brazil, with forwarding of all
the data used, being answered by PCI that there was no failure or problem. It is therefore
understood that the ASTERDTM modeling - which is a specialized ASTER module - is more
appropriate.
6.3. ALOS/AVNIR-2: Planimetric assessment of orthoimage
The ALOS/AVNIR-2 data, as well as those of the PRISM sensor of the same satellite, are of
great interest for Brazil, since its data was distributed by IBGE (
Instituto Brasileiro de
Geografia e Estatística
) for noncommercial users at a much lower price than those practiced
by the market for products with the same features. It remained to know its accuracy in order
to be able to fully explore its real capacity. The AVNIR-2 sensor acquired data in 4 spectral
bands (blue, green, red and near infrared) with a spatial resolution of 10 m. Since the
satellite contained a very advanced set of orbital and altitude control systems, its use would
be very appropriate both for reference as for thematic cartography.
The results presented here refer to the work published by a group of IBGE employees in [19]
who assessed the orthoimage geometry of this sensor.
Orthoimage was generated in Orthoengine 10.2, by PCI, with a resolution of 10 m, based on
a scene acquired with processing level 1B2R, making use of seven ground control points and
DEM SRTM version 4.0. The control points and the 34 assessment points were obtained
from orthoimages in scale 1:25,000 generated by IBGE from photos in the scale 1:35,000. This
