Saturday, June 6, 2015

Satellite SAR radar for mapping changes in global forest cover

Color composite image showing four-year variation
of forest cover in western Indonesia and Malaysia.
Global mosaics show phased-array type L-band synthetic aperture
radar-2 color composites in (top) horizontal transmission/ reception
(HH), horizontal transmission/vertical reception (HV), and
HH/HV modes in red, green and blue, respectively, and (bottom)
the corresponding map of forest areas (green)/non-forest areas (yellow)
High-resolution satellite radar for mapping changes in global forest cover | SPIE Newsroom: SPIE
Masanobu Shimada, Takuya Itoh, Takeshi Motooka, Manabu Watanabe and Rajesh Thapa


ALOS-2 Overview
Japanese HII-A successfully launches ALOS-2 mission 
The PALSAR-2 aboard ALOS-2 is an L-band Synthetic Aperture Radar(SAR) sensor, a microwave sensor that emits L-band radio waves and receives their reflection from the ground to acquire information. Selecting the most suitable mode for an objective will maximize the effectiveness of monitoring works. The PALSAR-2 has three modes:
  • Spotlight mode -The most detailed observation mode with 1 by 3 meters resolution (observation width of 25 km)
  • Strip Map mode - A high-resolution mode with the choice of 3, 6 or 10 meters resolution (observation width of 50 or 70km)
  • ScanSAR mode -A broad area observation mode with observation width of 350km or 490km, and resolution of 100m or 60m respectively
L-band SAR backscatter provides the basis of information regarding forest and non-forest areas on a global scale. The enhanced maps and classification of land use provide a new global resource for documenting the changing extent of forests and also offer opportunities to quantify historical and future changes through comparison with data from the Japanese Earth Resources Satellite-1 SAR (1992–1998) and ALOS-2/PALSAR-2 (from 2014). We have made four-year PALSAR mosaics and forest/non-forest data with 25m resolution freely available to the public.6 We also plan to distribute the original-resolution data sets from ALOS-2/PALSAR-2.

We first estimated the global forest area as 38,542,500km2 from the ALOS/PALSAR data set,4 following the Landsat-based estimation of forest area as 40,656,570km2.5 The difference can probably be attributed to a difference in the sensitivity of optical and L-band SAR techniques in measuring forest cover. Maps of forest/non-forest areas provide basic information for the interpretation of forest cover, so we anticipate the frequent generation of L-band SAR mosaics and related forest/non-forest maps from the forthcoming ALOS-2/PALSAR-2 data set.

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