1159 
SIMULTANEOUS IMPLEMENTATION OF A SYNTHETIC APERTURE 
RADAR AND A HIGH-RESOLUTION OPTICAL IMAGER 
AJ. SEPHTON 1 , M. CROSS 1 ,1. GREEN 2 , T. HAME 3 , K.-U. KOMP 4 , P.J. MEADOWS 1 , 
H. ROTT 5 , A. WIELOGORSKA 6 AND M. RAST 7 
(1) Space Division, Avionics Laboratory, GEC-Marconi Research Centre, 
West Hanningfield Rd., Great Baddow, Chelmsford, Essex, CM2 8HN (England) 
(2) Matra Marconi Space U.K., Anchorage Rd., Portsmouth, Hampshire, P03 5PU (England) 
(3) VTT, Vuorimiehentie 5, SF - 02150 Espoo (Finland) 
(4) EFTAS GmbH, Steinfurter Strasse 107, D - 48149 Munster (Germany) 
(5) Institute of Meteorology and Geophysics, University of Innsbruck, 6020 Innsbruck (Austria) 
(6) Hunting Technical Services Ltd., Thamesfield House, Boundary Way, 
Hemel Hempstead, Hertfordshire, HP2 7SR (England) 
(7) ESTEC, P.O. Box 299,2200 AG Noordwijk (Netherlands) 
ABSTRACT: 
In this work, which was managed by GEC-Marconi Research Centre under contract to ESTEC, the main aim is 
to determine for a number of application areas what are the temporal sampling requirements both for the 
acquisition of ‘added-value’ synergistic data (i.e. assuming no change in the underlying ground parameters), and 
to observe genuine change detection. Four main application areas are considered (vegetation, hydrology, 
cryosphere and geology / pedology), using a combination of cross-correlation and inversion techniques applied to 
a number of selected key parameters. Given that the different viewing geometries of SAR (side-looking) and 
optical (nadir) sensors would prevent the same area from being imaged simultaneously from the same platform, 
the resulting temporal sampling requirements are analysed to assess whether single-platform satellites 
combining SAR and optical sensors would be feasible in future missions for the various application areas 
considered. The results indicate that single-platform satellites could be used for such application areas. 
KEY WORDS: Microwave, Optical, Synergy, Contemporality, Temporal Sampling Requirements. 
1 - INTRODUCTION 
High resolution, spacebome, optical satellite sensors (e.g. SPOT, LANDSAT) have been in use for many years 
in the field of Earth Observation monitoring. Now that Synthetic Aperture Radar ('SAR') data is becoming 
routinely available, both from ERS-1 and the proposed launch of further SAR systems (e.g. ERS-2, ENVISAT, 
RADARSAT), ‘synergistic’ studies for the retrieval of ground-based, geophysical parameters are appropriate. 
If a well-defined relationship exists between a common parameter derived from data from 
different sensor types, then ‘synergy’ can be considered to be simply the interpolation of gaps in data coverage, 
perhaps due to cloud cover or mission requirements such as orbit geometry, power limitations, data-rate, etc. In 
this instance, there is effectively no gain in data content over using only one type of instrument sensor onboard 
a number of satellites. However, the different characteristics of data recorded by sensors operating in different 
parts of the electromagnetic spectrum in principle enable additional information to be derived, beyond the 
capabilities of one type of sensor by itself. Thus, the high sensitivity of microwaves to water content and 
surface roughness may enable the differentiation of land-use classes not distinguishable in the visible spectrum 
alone.