International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B4. Istanbul 2004
3. CHARACTERISTICS OF HIGH RESOLUTION
DIGITAL IMAGES AND REFERENCE MAPS
The experiment was carried out on six high resolution satellite
images, two of which were taken from the IKONOS II satellite
on the municipal territory of Palermo and Contessa Entellina;
the other five images, were acquired by the QuickBird satellite,
on the territories of Palermo, Scopello, Contessa Entellina and
Caselle Torinese. IKONOS images are Geo Product type. The
IKONOS Geo Product is a low-accuracy georeferenced
product. The features of these images are showed in the table 1.
Data pre-processing consists in a geometrical correction in
order to remove the distortions introduced by the acquisition
geometry. The re-sampling of the image is carried out imposing
a constant ground sample distance, as well as the arrangement
in a specific datum and map projection. The circular error
(CE90) of this IKONOS product type is about X15 m. Table 1
describes the most important characteristics of the IKONOS
Geo images. QuickBird images are Standard type for the three
Sicilians areas and Basic type for the Caselle Torinese area.
Standard Imagery products are radiometrically corrected,
sensor corrected, geometrically corrected, and mapped to a
cartographic projection. Standard Imagery has a coarse DEM
applied to it, which is used to normalize for topographic relief
with respect to the reference ellipsoid. The degree of
normalization is relatively small, so while this product has
terrain corrections, it is not considered orthorectified. The
Circular Error (CE90) for this product line is about £23 m.
Basic Imagery products are the least processed of the QuickBird
Imagery Products and are designed for customers having
advanced image processing capabilities. Basic Imagery,
together with the supplied attitude, ephemeris, and camera
model information, is suitable for advanced photogrammetric
processing (QuickBird Imagery Products — Product Guide).
Table 2 shows the most important characteristics of the
QuickBird images.
Contessa Palermo
Entellina (PA)
Type GEO Pan GEO Pan
Acquisition Date 01/06/2000 06/04/2002
Sensor elevation 84.50231° 60.78805°
Sensor azimut 220 6225 0.1336?
Sun elevation 66.58229° 139.1573?
Sun azimut 125.8465? 70.61002°
RadiometHic 11 bit 11 bit
resolution
Geometric
: 1m 1m
resolution
Datum UTM-WGS84 | UTM-WGS84
9553 pixel x 10248 pixel x
; ; 9495 pixel 11804 pixel
Dimentions 9553 m x 10248 m x
9495 m 11804 m
Table 1. Characteristics of the IKONOS Geo images
The following maps were used in the described experiment:
- Palermo - raster map at a scale of 1:2000 and raster map at
scale 1:10,000 (Regional Map);
- Contessa Entellina - raster map at a scale of 1:5000 and vector
map at scale 1:10,000 (Regional Map);
- Scopello - raster map at a scale of 1:25,000 and raster map at
scale of 1:10,000 (Regional Map);
- Caselle — raster map at a scale of 1:5000 provided by the
Province of Torino.
594
Entellina (PA) Scopello Palermo Caselle (TO)
Type Standard Standard Standard Basic
Acquisition Date | 17/07/2002 11/06/2002 01/02/2002 26/09/2002
Sensor elevation 80.5597" 80.6412° 68.8072° 78.4815°
Sensor azimut 31.3294° 105.7075° 87.0227° 249.016°
Sun elevation 66.6436° 68.6976° 62.0918° 325551
Sun azimut 129.076° 128.8707° 139.947° 159.251°
Radiometric ; ; ; ;
resolution 16 bit 16 bit 16 bit 16 bit
Geometric
resolution Qo 70m 070m 070m 062m
Datum UTM-WGS84 | UTMWGS84 | UTM-WGS84 | UTM-WGS84
7260 pixel x | 7148pixel x | 7240 pixel x | 28684 pixel x
: : 7176 pixel 7546 pixel 7260 pixel 27552 pixel
Dimpntions 502mx | 5003mx | 5068mx | 17784m x
5023 m 5284 m 5082 m 17082 m
Table 2. Characteristics of the QuickBird images
4. GROUND CONTROL POINTS AND CHECK POINTS
Ground Control Points (GCPs) and Check Points (CPs)
necessary to orthorectify the satellite images and to control the
orthophotos accuracy, were collected both by using GPS
method (Smith D. P., Atkinson S. F., 2001) and by extracting
point coordinates from high scale maps.
The points surveyed with GPS were previously identified on the
images then, verified the possibility of standing on the ground,
a static-rapid method was employed with acquisition time of
about 20' and rate of 5", by using three double-frequency
Topcon Legacy-H GPS receivers.
A well-distributed pattern of points was selected spaced
uniformly throughout the study area. Where possible, the points
were located on the country plain close to artificial elements
(corner of pavements and flowerbeds, crossroads, outcrop of
rocks). The accuracy of their coordinates was in order of few
centimetres. Extracted data were processed in WGS84 reference
system, by using Pinnacle 1.0 software. Subsequently all the
coordinates were transformed in the National Map System
(Gauss-Boaga), using a seven parameters transformation
available from the points of the IGM95 National GPS network
closer to test sites.
A part of the control points and check points was extracted by
the official maps which had a larger representation scale than
the one of the digital ortophotos.
On the whole, 70 points were considered both on the territory of
Palermo and Contessa Entellina, and 60 points on the territory
of Scopello. For the Caselle image a set of 18 points, equally
divided in GCPs and CPs, was used.
5. ALTIMETRIC DATA
The DEMs used to ortorectify images were extracted from the
reference maps.
Particularly, for the territory of Palermo and Contessa Entellina
two DEMs were produced by digitalization of the contour lines
of the Regional Map and interpolation with a grid-cell of 10
meters.
For the Scopello area, a DEM was produced by digitalization of
the contour lines of a maps at scale 1:25,000 with grid-cell of
50 meters.
Finally a DEM with a grid-cell of 40 meters was used to
orthoproject the QuickBird Basic image of Caselle Torinese
(TO).
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