Cambodia March 2012

Cambodia February 2012

These two mosaics (February & March 2012) were produced from a 18 ASAR ENVISAT Images processed as follows:

Red is HH polarization
Green is HV polarization
Blue is ratio of HH/HV

To interpret the mosaic colors:

Green areas on the mosaics indicate presence of vegetation (forest, rice paddy etc.)
Blue areas indicate wetter open soils with minimal vegetation.
Red areas indicate drier open soils with minimal vegetation.
White/Yellow indictes human settlements

ENVISAT was a European Satellite that operated for almost a decade building up an extensive archive of imagery before unfortunately going "dead" in April 2012. It's replacements, the first two Sentinel satellites (1 & 2) are expected to be launched in 2013. 

In total 120+ ENVISAT ASAR images have been processed so far using this color combination.
The two monthly mosaics shown were chosen as examples as there is almost complete national coverage
for these two months in the ESA archives. Radar satellite is especially useful in a country such as Cambodia
for many reasons:

1) Cambodia is relatively flat and therefore terrain effects that complicate the analysis of radar imagery are minimal.

2) During the wet season Cambodia has extensive clouds that block the use of optical satellites however
radar can see through the clouds. For this reason radar is particularly useful for flood emergenices.

3) Mapping of Cambodian dry forest types from optical satellites such as Landsat have difficulties as the only available imagery during the dry season is when the leaves are off the trees.

4) It is possible to directly estimate vegetation biomass from radar back-scatter. Indeed the ESA supported "Dragon Project" has recently updated a biomass map of the whole of the Greater Mekong Subregion as well as China using this method.

5) Radar can be used to generate a high resolution digital elevation model that may also give some estimate of average tree height in a forest. 

6) Some geological structures can be more readily discerned compared to say Landsat imagery.

7) Relatively frequents satellite re-visit times (unblocked by clouds) make it possible to more closely monitor agriculture crops or activities causing deforestation. 

Imagery is from February 2012 & March 2012 respectively
(with 3 images used from January 2012 to fill small gaps.)
Current ASAR mosaic pixel resolution is about 75 meters.
Higher resolution mode ASAR imagery is also available at about 12.5 meter
resolution for some areas (especially around Phnom Penh and central Cambodia/Mekong)

Higher resolution zoom of Phnom Penh Area in March 2012 follows: 

Phnom Penh March 2012