An overview of the JERS-1 SAR
Global Boreal Forest Mapping (GBFM) project
A. Rosenqvist1, M. Shimada1, B. Chapman2, K. McDonald 2, G. De Grandi 3, H. Jonsson4
C. Williams5, Y. Rauste6, M. Nilsson7, D. Sango8 and M. Matsumoto8
1

Japan Aerospace Exploration Agency, EORC, Harumi 1-8-10-X23F, Chuo-ku, Tokyo 104-6023, Japan2
Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
3
Joint Research Centre of the E.C., IES/GVM, TP 440, 21020 Ispra (VA), Italy
4
National Land Survey/Metria, P.O. Box 24154, 104 51 Stockholm, Sweden
5
Alaska Satellite Facility, Univ. Alaska Fairbanks, P.O.Box 757320, Fairbanks, AK, USA
6
VTT Information Technology, P.O. Box 1201, 02044 VTT, Espoo, Finland
7
Swedish National Space Board, P.O. Box 4006, 171 04 Solna, Sweden
8
Remote Sensing Technology Center of Japan, Harumi 1-8-10-X21F, Chuo-ku, Tokyo 104-6023, Japan

Abstract - Boreal ecosystems play an essential role in global
climate regulation. Forests constitute pools of terrestrial carbon andare generally considered as global sinks of atmospheric CO2,contributing to attenuating the greenhouse effect. Large amounts ofcarbon are also stored in boreal lakes, bogs and wetlands, partiallyreleased as CH4 and other trace gases to the atmosphere during thespring and summer months. Human activities in the forest zone are
however reducing the size of the carbon pool and climate change istriggering shorter winters and earlier thaw onset, changing the naturalequilibrium. Given its global importance, there is a need to map andmonitor the boreal zone, and as the changes occur on all from local,
regional to global scales, fine resolution information over vast areas
is required.
The Global Boreal Forest Mapping (GBFM) project is aninternational collaborative undertaking initiated by NASDA in 1996,
as a follow-on to the tropical-focused Global Rain Forest Mapping(GRFM) project [1]. Utilising the L-band Synthetic Aperture Radar(SAR) on the Japanese Earth Resources Satellite (JERS-1), one of themain objectives of the GBFM project is the generation of extensive,
pan-boreal, SAR image mosaics, to provide snap-shots of the forest-,
wetland and open water status in the mid-1990’s. Mosaics overCanada, Alaska, Siberia and Europe have been generated, available
on the Internet and on DVD free of charge for research andeducational purposes.
The GBFM project also entails research activities in North
America, Siberia and northern Europe, aimed at advancing scientificapplications of L-band SAR data in the boreal zone.

1. BACKGROUND
1.1 GBFM Partners
The Global Boreal Forest Mapping (GBFM) project is led
by the Earth Observation Research and applications Center(EORC) of the Japan Aerospace Exploration Agency (JAXA),
but relies strongly on international collaboration. The NASA
Jet Propulsion Laboratory (JPL), in cooperation with theAlaska Satellite Facility (ASF), is responsible for mosaic andapplications development in North American zone, while theE.U. Joint Research Centre (JRC), in cooperation withVTT/Finland, are in charge of Siberia and Europe.
A regional research programme for Northern Europe,
funded by the Swedish National Space Board (SNSB), wascarried out 1997-2002 by the National Land Survey/METRIA.

1.2 The JERS-1 satellite
The Japanese Earth Resources Satellite (JERS-1) waslaunched by JAXA (then, NASDA) in February 1992, staying
in operation for 6.5 years, until October 1998. It carried an Lband (1275 MHz/23.5 cm) SAR which operated with HHpolarization and a fixed 35° off-nadir angle. Satellite repeat
cycle was 44 days, with an image swath of 75 km.
Several features made JERS-1 particularly suitable forforest monitoring, most notably the low L-band frequency,
which is more sensitive to vegetation structure than other (Cband) SAR instruments in orbit. L-band signals are also
sensitive to standing water below the forest canopy - a uniquecharacteristic among all contemporary earth observation
satellites (both optical and microwave). A distinctive featureof JERS-1 was also that its orbit was designed so that adjacentpasses were acquired on consecutive days. This results in an
optimal 1-day time difference between neighbouring passes,
and hence the capacity to acquire temporally homogeneous
data even over large areas.

1.3 Pan-boreal SAR observations
Fine resolution remote sensing data are traditionally notacquired homogeneously over large areas, but instead
typically collected with local focus over specific sites
extending over one or a few scenes. Such approaches result ininconsistent and fragmented data archives that are inadequate
for any application that requires extrapolation of locallydeveloped methods and results to a regional or global scalecontext.
The importance of acquiring data in a spatially andtemporally uniform manner over large regions was first
demonstrated within the tropical GRFM project [1], whereJERS SAR data were acquired with temporal and spatialconsistency over the tropical belt of the Earth, enabling thedevelopment of unprecedented, regional-scale applications.
Building on this experience, the acquisition plans for
Siberia, Europe and North America were designed for two
seasonal covers – summer and winter – with acquisitions
initiated during summer 1997 and continuing through thefollowing winter, into summer 1998.

2. GBFM MOSAIC GENERATION
2.1 Boreal North AmericaFigure 1. 100 m JERS-1 SAR mosaic coverage over North America.
(a – upper) Summer, 1997. (b – lower) Winter, 1997/98
GBFM © JAXA/JPL/JRC

In order to reduce the total amount of JERS-1 SAR data to
be acquired (by a factor 2), the GBFM observation plan
focused on the circum-polar region north of latitude 54°,
above which the extensive overlap between neighbouring
swaths allowed the collection of every second – rather thaneach – satellite pass with maintained across-track coverage.
For acquisitions which extend below N 54°, originally notplanned to be utilised within the project, gaps between thepasses become evident (Fig. 1a).

The North American component of the GBFM project
covers the region of Alaska and most of continental Canada.
The central and eastern Canadian coverage was dependent on
the JERS-1 tape recorder operations and as a result, the mostcomplete coverage was achieved during the summer of 1997,
with fill-in data drawn primarily from 1994 and 1995 (Fig.
1a). The winter coverage is less comprehensive and was put
together using archived data from, chiefly, the 1994/95,1995/96 and 1996/97 seasons (Fig. 1b east). Much better
coverage was achieved over the region covered by the Alaska
Satellite Facility (ASF) ground station, over which nearcomplete seasonal coverages for the winter of 1997/98 and thesummer of 1998 could be acquired. (Fig. 1b – west)
Raw data processing of all North American GBFM data
was performed by ASF, who processed over 16,000 scenes tosupport the mosaic assembly. The Jet Propulsion Laboratory(JPL) in turn, was in charge of geometric and radiometric post
calibration of the SAR data and ensuing, generation of thecorresponding SAR image mosaics. Drawing on the multiyear database, 2,085 winter scenes and 3,076 summer scenes
were assembled to create the mosaics. The mosaicking
software used was a modified version of the code developedby JPL for South America within the GRFM project [2].
In order to maintain highest radiometric quality, fullresolution scene products (ground range, 4 looks, 12.5 mpixels), filtered to 100 m spatial resolution by block averaging,were used as base for the mosaic development, in which also
texture (coeff. of variation) mosaics were generated.
Finalized in late 2002, the multi-season backscatter andtexture mosaics are given in Albers Equal Area projection
with a pixel spacing of 100 metres. More background on theNorth American GBFM component can be found in [3-7].

1.4 Tape recorder operations
Equipped with an on-board tape recorder, JERS-1 had thecapacity for fast data access and full coverage also overregions without ground receiving stations. Having exceeded its
designed life-time with several years however, raising bit error
rates during recorder playback increasingly started to have adirect negative impact on data downlink, and the tape recordersubsequently had to be taken out of operations in September
1997, before the planned wall-to-wall winter acquisitions
could commence. Without doubt, this caused a set-back for theproject, which thus had to rely on non-complete archived data
for the winter coverages (as illustrated for eastern Canada inFig. 1b). In the case of Siberia, plans for dual-season mosaics
had to be abandoned altogether as sufficient data for asatisfactory winter coverage could not be assembled.

Figure 2. Multi-temporal GBFM mosaic over Alaska (R:1997 summer;
G: 1997/98 winter; B: 1997 summer- texture). GBFM © JAXA/JPL/JRC

Figure 3. 100 m JERS-1 SAR mosaic over Siberia (1997).
(incomplete draft). GBFM © JAXA/JRC/JPL

2.2 Siberia and Europe
The JERS-1 coverage over the Eurasian continent arcs
over some 210 longitude degrees along the coast of the Arctic
Sea, from Bering Strait and Kamchatka in the east, to Iceland,Ireland and Portugal in the west.
The Siberian half, east of the Ural Mountains, covers mostof the territory of Asian Russia, north Mongolia, and northeast
China, encompassing an area of roughly 20 million km2.
About 80% of the JERS data used within the project wereacquired between April and September 1997, during which theon-board tape recorder was drawing its last breaths. The
remaining data were obtained from the JERS 1993-1996
archives, with preference for summer data when available, tominimize seasonal-induced backscatter differences in theresulting mosaics. Less than 3% of the data used wereacquired during any of the months of October through March.
The European half extends from Norwegian Nordkapp
well below the boreal zone to cover all of western and centralEurope, as far as the islands of Malta and Cyprus in theMediterranean. More than 80% of the data used were acquired
between May 1997, and August, 1998 – a significant part of itby the ground stations operated by the European Space
Agency, ESA. About 15% of the European coveragecomprises of winter (October -March) data.
Raw signal processing of all SAR data, including the shareacquired by ESA, were performed by JAXA, using theSIGMA-SAR processor developed at the EORC [8]. In
contrast to the scene-based processing performed for the North
American component, the Eurasian JERS data were processedto continuous swath images, some 80 km wide and up to 2500
km long.
The E.U. Joint Research Centre (JRC) in Ispra, Italy,
in collaboration with Finnish VTT Information Technology,
was responsible for the generation of the Eurasian mosaics.
Based on algorithms developed by the JRC within the GRFM
framework for calibration and generation of JERS-1 mosaics

Figure 4. 100 m JERS-1 SAR mosaic over Europe (1997/98).
(incomplete draft). GBFM © JAXA/JRC/JPL

over Africa [9], the software was modified to comply with
continuous path data and extensive, non-linear overlap
between passes. 100 metre pixel spacing path images generated from full resolution (18 m) path data by B-spline
filtering – were used as input in the global block adjustment
programme, which is described in detail in [10, 11].
Some 535 passes were required for the full Eurasianmosaic, corresponding to approximately 8500 JAXA standard(75*75 km) scenes, or 6300 ASF-size (75*100 km) scenes.
Figure 3 and 4 show draft versions of the mosaics – stillincomplete with significant data gaps - but illustrating theirextreme geographical coverage. In agreement with their North
American counterparts, also the Eurasian mosaics –backscatter and radar texture – are produced in Albers Equal
Area projection, with a pixel spacing of 100 metres.

2.3 GBFM Data Sets
All mosaics generated within the GBFM framework areavailable free of charge for research and educational purposes.
The North American data sets are presently available on DVD,and the corresponding Eurasian products are scheduled forcompletion and subsequent DVD distribution in late 2004.
To order a DVD, send an email request to JAXA
(aproject@eorc.jaxa.jp), JPL (kyle.mcdonald@jpl.nasa.gov) or
the JRC (frank.de-grandi@jrc.it).
Low resolution versions of the mosaics (500 m and 2 km)
are available on the Internet for browsing and downloading at:
JAXA: http://www.eorc.jaxa.jp/JERS-1/
JPL:
http://southport.jpl.nasa.gov/GBFM

2.4 The North European Research Programme
While no official PI programme was undertaken by JAXA
within the framework of GBFM, a small regional research
programme for Northern Europe, funded by the Swedish
National Space Board (SNSB) and managed by the National
Land Survey/METRIA, was initiated in 1997 to stimulate andadvance L-band SAR research and applications development
relating to boreal forestry in Northern Europe [12]. The
announcement attracted 13 investigators, out of which 9
completed their projects. As no mosaic data were available atthe time, research projects were performed on a local-scale,using standard fine resolution scene products.
The research programme was concluded with aworkshop held in Stockholm in February 2002. Proceedings
from the meeting are published on CD-ROM [13], and areavailable on request from SNSB (maria.nilsson@snsb.se) orMETRIA (hans.jonsson@lm.se).

3. CONCLUSIONS

4. REFERENCES
[1]

[2]

[3]
[4]

[5]

[6]

3.1 Summary
Spanning around the entire boreal zone from Canada, via
Siberia, to Iceland, the GBFM mosaics represent, without
doubt, one of the most extensive sets of fine resolution
mosaics ever created. As full resolution imagery were used as
basic input data, the effective number of looks for each 100 mpixel exceeds 200, hence making the GBFM mosaic
radiometry distinctly superior to that of mosaics with similar
pixel spacing, but assembled from e.g. ScanSAR data.
The potential shortcomings of the GBFM data sets rather
lie in the incomplete spatial coverage and temporal inhomogeneities, which nevertheless prevail over certain areas, thus
highlighting the need for a concept change in mission
planning.

[7]

[8]
[9]

[10]

3.2 Future prospects
Taking lesson from the JERS-1 experience, JAXA isimplementing an entirely new acquisition strategy for theforthcoming Advanced Land Observing Satellite (ALOS) [14].
Focusing on achieving regional- to continental-scaleconsistency in both time and space, dedicated observation
schemes are being implemented for all three sensors(PALSAR, PRISM, AVNIR-2) in which all land areas are to
be acquired on a repetitive basis during the lifetime of ALOS.
Abandoning traditional, local-focused instrument operations,which result in scattered and fragmented data archives, theaim is set on providing time series of regionally consistent
data which allow multi-resolution, multi-scale analysis.
As a follow-on to the GRFB/GBFM activities, JAXA has
initiated a new international collaborative project for ALOS the Kyoto & Carbon Initiative – set out to exploit the ALOS
systematic archives to provide better tools to address climatechange,multinational
conventions,environmental
conservation and other cross-border issues of public interest[15]. Amongst others, global 50 m dual-polarization PALSAR
mosaics are in the pipeline. Stay tuned…

[11]

[12]

[13]
[14]

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