In the case of forests, Pol-InSAR typically relies on longer L- or P- band wavelengths upon in preference to the shorter C-band wavelengths used by the radar satellites currently in orbit - these code letters being a legacy from radar's wartime origins.
Envisat's C-band radar has a wavelength of 5.8 centimetres, which is too short to pierce through a dense forest canopy. Instead Pol-InSAR measurements are made using L- and P-band wavelengths, which range between around 15 to 100 cms closer to the dimensions of the trees researchers are interested in.
The E-SAR sensor used during INDREX-II has multi-polarisation X-, C- L- and P-band wavelengths available. Hensley's team has been surveying tropical forests in Costa Rica with the AIRSAR airborne instrument, similarly with multi-polarisation C-, L- and P-band wavelengths.
Putting Pol-InSAR into space?
Pol-InSAR is a relatively young field, albeit one that has come on greatly since the first POLINSAR workshop at ESRIN back in January 2003. That meeting concluded with recommendations that Pol-InSAR be tested on further forest types, which led to the INDREX-II campaign.
This time discussions were centred on the prospect of the current generation of airborne sensors eventually making it into orbit aboard to a Pol-InSAR-capable satellite.
There are several new radar missions due to enter service - including Germany's TerraSAR-X, Japan's Advanced Land Observing Satellite (ALOS), the Italian-French CosmoSkyMed and Canada's Radarsat-2 but while they offer researchers an increased range of radar wavelengths and polarization combinations, none are optimised for Pol-InSAR.
A major hindrance is that a single satellite can take time to revisit the same area 35 days in the case of Envisat. In just a few days between images, vegetation growth in forested areas can be so great to prevent
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Contact: Mariangela D'Acunto
mariangela.dacunto@esa.int
39-069-418-0856
European Space Agency
1-Feb-2005