GRFM - Insular South-East Asia (SEA-2) Data Products

This CD-ROM set contains  JERS-1 SAR mosaics covering the insular part of South-East Asia, including Indonesia, Malaysia, Singapore, Brunei, East Timor, the Philippines, Papua New Guinea and the Solomon Islands. The mosaics are available at 100 m, 500 m and 2 km pixel spacing.

JERS-1 SAR data processing and mosaic assembly

SAR data processing and mosaic assembly were performed by the JAXA Earth Observation Research and applications Center (JAXA EORC) in Tokyo, Japan.

The raw JERS-1 SAR data were processed with JAXA's Sigma-SAR "strip mode" processor, in which the full 75 km wide satellite swaths were processed as continous data sets, sometimes as long as 3000 km. All data passes were initially processed to full spatial resolution (18 metres, 4 looks) to maintain radiometric quality, and in the subsequent mosaicking step, resampled by averaging to 100 metre pixel spacing. The mosaics were generated strip by strip from east to west, using image matching and correlation in the overlap zones between adjacent passes to maintain geometric accuracy.

To reduce file sizes and better accommodate data display, the large mosaics were compressed from 16 bits to 8 bit files (scale factor 50, offset factor 1000) and subsequently divided into smaller rectangular regions - here referred to as tiles - typically some 5 by 5 degrees in size. Adjacent tiles fit exactly along side one another without overlap (with the exception of tile 6, which overlaps 20 km with tiles 5, 10 and 12), and can easily be "re-mosaicked" using some GIS or image processing software. The corner coordinates of each tile are given here.

Low resolution mosaics at 500 m and 2 km pixel spacing are also available here, generated through block-averaging of the (16 bits) 100 m resolution mosaic data. These low resolution data are provided both as tiles - identical to the 100 m tiles in terms of geolocation and coverage - as well as complete mosaics. The tiles are linked from a clickable tile map, or via a table, and can be viewed either with the web broswer you are currently using, or with any GIS or image processing software.

In addition, low resolution texture mosaics are also featured on the CD-ROM set, corresponding in geometry to the 500 m and 2 km resolution complete mosaics. The texture measute used here is the simple coefficient of variation, cv, which is defined as the standard deviation (of the radar amplitude) divided by its mean value for all 100 m pixels within a 5x5 (20x20) pixel window.

A detailed description of the mosaicking prcedure can be found in Shimada and Isoguchi (JERS-1 SAR mosaics of Southeast Asia using calibrated path images, International Journal of Remote Sensing, 2002, Vol.23, No.7, pp.1507-1526), available as pdf here.

Mosaic projections

Mercator projection

The map projection used for the mosaics on this CD-ROM set is the traditional Mercator projection.

In Mercator, the Earth's surface is projected onto a cylinder which tangents the Earth along the Equator. Mercator should be distinguished from the Universal Transverse Mercator, UTM, in which the projection cylinder tangents the Earth along a meridian, or longitude line. Hence, in Mercator there is thus no central meridian, but rather a central latitude, represented by the Equator.

Mosaic projection: Mercator
Ellipsoid: GRS-80
Geodetic datum: GRS-80
Latitude of true scale: 0.0 deg.

Geographical coordinates

While all tiles (100 m, 500 m and 2 km) are given in Mercator projection, the 500 m resolution complete mosaics are provided both in Mercator projection, and in addition in non-projected geographcal lat/long coordinates, to accommodate GIS users.

The geographical coordinate versions of the 500 m mosaics, have a constant pixel spacing in latitude and longitude direction of 15 arc-seconds, which at the Equator corresponds to a pixel spacing of approximately 463 m.

Radar backscatter (Sigma0)

The DN pixel values of the mosaics represent the radar backscatter, or the normalized radar cross section, sigma0, which can be computed as:

sigma0 = 20*log10(50*DN100m+ 1000) + F  [dB] 

where DN is the digital value of each pixel, and F is the radar calibration factor. For the data on this CD-ROM set, F = -84.66 dB. The numbers 50 and 1000 were used as scaling and offset factors in the 16 to 8 bit compression. 

Mosaic temporal composition

The number of JERS-1 acquisitions and temporal composition of each blanket coverage varies between the  different island regions. The predominant time windows for each of the coverages is given below, while a detailed list of the acquisition dates of each of the individual passes used is given in the table of acquisition dates.

Sumatra & Peninsular Malaysia
(1) March, 1993
(2) June - July, 1998

Java, Borneo, Sulawesi & the Lesser Sunda islands
(1) September - November, 1994
(2) October - November, 1996
(3) July - September, 1998

The Philippines
(1) December, 1996

New Guinea island
(1) January - April, 1996

The Moluccas
(1) February - November, 1996

The Solomon Islands
(1) Assorted 1992-1996