Internat 
A RIGOROUS MODEL AND DEM GENERATION FOR SPOT5 —HRS The 
for the 
from 
Pantelis Michalis and Ian Dowman 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
HRS 
Department of Geomatic Engineering, University College London, Gower Street, whole 
London WCIE 6BT, UK | distrib 
[pmike,idowman]@ge.ucl.ac.uk 
Commission I 
4.1 A] 
KEYWORDS: Sensor modelling, along track satellite imagery, DEM 
| | 4.1.1. 
ABSTRACT | the U( 
the re 
This paper describes a new model developed at UCL for along track stereo sensors. The model is tested on SPOT HRS data rigoro 
provided under the SPOT Assessment Project (SAP) set up by CNES and ISPRS. The SPOT HRS data has been used to test a new assum 
sensor model for along track satellite data, and to generate a DEM using the Leica Photogrammetry Suite (LPS). The model . Th 
described in this paper uses the collinearity equations in combination with astrodynamics. The main and fundamental point during to | 
the development of this model was to benefit from acquisition in the same orbit. The collinearity equations are modified to model the » Th 
characteristics of a pushbroom scanner and the number of exterior orientation parameters. The state vector at the origin point of each col 
image is computed. The results of testing the model with HRS data show that the model provides a stable, accurate and rigorous | flis 
solution. The solution for the orientation from the LPS gives similar results to the new model and generates a DEM of a es A 
mou: ^inous area which is within the expected accuracy of SPOT HRS data. The model can be used for any along track satellite dir 
sens: lin 
; pai 
I. INTRODUCTION 2.3 Metadata | po 
| CAS 
Since the SPOT series of satellites were first launched in 1986, The SPOT > HRS Level LA product is delivered in DIMAP | = Th 
many models for push room sensors have been developed, some format which is the standard format for SPOT 5 products. dir 
explicitly for along track sensors, designed to make use of data | = At 
acquisition of both images from the same orbit. However little 3. REFERENCE DATA | Cal 
work has been directed to the generation of DEMs from along : : ) Fh 
track stereo sensors. This paper describes the development and The test area is located around Aix-en-Provence in SE France | col 
testing of a model derived specifically for along track sensors and covers [GN map sheet 3244. The area is shown on Figure | res 
and for the generation of a DEM from SPOT HRS data provided d l'he data was made available to the CEOS WGCV Terrain | + Du 
by the SPOT Assessment Project (SAP) set up by CNES and Mapping WG by permission of UCL and IGN. A number of ma 
ISPRS. tests have been carried out over this site on different types of pic 
data. | 
2. SPOT 5 : 4344 | A sp 
2.1 SPOT 5 Mission IGN 50m 3243 | using 
3143 ries RPM | also u 
SPOT 5 is the latest satellite of the SPOT family, launched during D HA 43°34 | point 
the night of the 3rd to the 4th of May 2002. This satellite ensures ; i uct. PITKIN | Keple 
data continuity with the previous satellites but provides also 3144 3244 Ë ; | image 
enhanced images (at 2.5 m resolution with its two HRG IGN 10m | | betwe 
instruments) and new stereoscopic capabilities with the HRS : 4323 | model 
instrument. A star tracker is used to get better attitude | are co 
measurements and therefore better image location (Baudoin et al, 3145 3245 | 
2003). A312? | 4.1.2 | 
—M M net | model 
2.2 HRS instrument SPOT E | soluti 
S a = | * d 
The High Resolution Stereoscopic instrument (HRS) has two i a im | me 
telescopes and acquires Stereopairs at a 90-second interval, of | dt 
120-km swath, along the track of the satellite, with a B/H ratio of Figure 1. The test site inc 
about 0.8. (Baudoin et al, 2003). Forward and backward u 
acquisitions cannot be performed at the same time. As a The following DEMs are available: ex 
consequence, the maximum stereo segment that can be acquired On th 
is a little bit more than 600 km (« 832 km altitude x 2 x tan(209)). Source UCL Pitkin IGN IGN med 
Forward and backward images are obtained in the same ; which 
panchromatic spectral band as for HRG. The size of the pixels on 30m 30m 10m solve 
hy ground is 10m x 10m. However, the HRS instrument has been Rmse +1.3m 5-2.5m Im ay 
esigned for a ground sampling distance of 5 metres along the Source ; : A 
track. In a direction close to the epipolar planes, this ERE UC sors Aerial Aerial Ae iene 
over-sampling allows higher altimetric accuracy of the DEM to Extent (km) 124x6.9 61 x 63 306x217 any, 
be obtained (absolute planimetric resolution from 10 to 15 of eac 
meters). Table 1. Reference DEM