This paper describes the tower-based radar BorealScat, which is being developed for polarimetric, tomographic and Doppler measurements at the hemi-boreal forest test site in Remningstorp, Sweden. The facility consists of a 50-m high tower equipped with an antenna array at the top of the tower, a 20-port vector network analyser (VNA), 20 low-loss cables for interconnection, and a calibration loop with a switching network. The first version of BorealScat will perform the full set of measurements in the frequency range 0.4-1.4 GHz, i.e. P-band and L-band. The tower is currently under construction at a forest stand dominated by Norway spruce (Picea abies (L.) Karst.). The mature stand has an above-ground dry biomass of 300 tons/ha. Data collections are planned to commence in autumn 2016

Eriksson, Leif E.B.

Fransson, J. E. S.

Monteith, Albert

Persson, H. J.

Soja, Maciej J.

Ulander, Lars M. H.

Ulander, Lars

Soja, Maciej

Eriksson, Leif

Persson, H.

Chalmers Research

Borealscat: A tower experiment for understanding temporal changes in P- and L-band backscattering from a Boreal forest

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Borealscat: A tower experiment for understanding temporal changes in P- and L-
band backscattering from a Boreal forest
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Citation for the published paper:
Ulander, L. ; Soja, M. ; Monteith, A. et al. (2016) "Borealscat: A tower experiment for
understanding temporal changes in P- and L-band backscattering from a Boreal forest".
European Space Agency, (Special Publication). Living Planet Symposium 2016, Prague,
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(article starts on next page)
 BOREALSCAT: A TOWER EXPERIMENT FOR UNDERSTANDING TEMPORAL 
CHANGES IN P- AND L-BAND BACKSCATTERING FROM A BOREAL FOREST 
 
Lars M.H. Ulander (1), Maciej J. Soja (1), Albert R. Monteith (1), Leif E.B. Eriksson (1), Johan E.S. Fransson(1), and 
Henrik J. Persson(2) 
(1) Chalmers University of Technology, Dept. of Earth and Space Sciences, SE-412 96 Gothenburg, Sweden,  
Email: lars.ulander@chalmers.se, maciej.soja@chalmers.se, monteith@chalmers.se, leif.eriksson@chalmers.se 
(2) Swedish University of Agricultural Sciences, Dept. of Forest Resource Management, SE-901 83 Umeå, Sweden,             
Email: johan.fransson@slu.se, henrik.persson@slu.se 
 
ABSTRACT 
This paper describes the tower-based radar BorealScat, 
which is being developed for polarimetric, tomographic 
and Doppler measurements at the hemi-boreal forest test 
site in Remningstorp, Sweden. The facility consists of a 
50-m high tower equipped with an antenna array at the 
top of the tower, a 20-port vector network analyser 
(VNA), 20 low-loss cables for interconnection, and a 
calibration loop with a switching network. The first 
version of BorealScat will perform the full set of 
measurements in the frequency range 0.4 – 1.4 GHz, i.e. 
P-band and L-band. The tower is currently under 
construction at a forest stand dominated by Norway 
spruce (Picea abies (L.) Karst.). The mature stand has 
an above-ground dry biomass of 300 tons/ha. Data 
collections are planned to commence in autumn 2016. 
1. INTRODUCTION 
Spaceborne mapping of forest biomass is an active 
research topic due to the lack of accurate estimates of 
global forest carbon stock, as well as the lack of suitable 
instrumentation for deforestation and forest degradation 
monitoring [1]. In May 2013, the BIOMASS mission 
was selected by the European Space Agency (ESA) to 
become the 7th Earth Explorer [2-4]. Equipped with the 
first P-band (432-438 MHz) synthetic-aperture radar 
(SAR) in space, the main objective of BIOMASS will 
be near-global monitoring and estimation of forest 
biomass and disturbance. During a dedicated phase at 
the beginning of the mission, BIOMASS will operate in 
a repeat-pass tomographic mode, giving information 
about the vertical distribution of backscattering in 
forests. However, due to ITU (International 
Telecommunication Union) regulations, BIOMASS 
coverage will be restricted over Europe and North 
America, leaving large areas of boreal forests 
unmonitored. To improve boreal forest mapping, ESA is 
currently investigating the implementation of a passive 
companion satellite to the Argentine SAOCOM-1B L-
band (1250-1300 MHz) SAR satellite. The SAOCOM-
1B companion satellite (SAOCOM-CS) mission will 
focus on mapping of the boreal forests using SAR 
tomography [5-6].  
 
Among the greatest challenges in forest parameter 
estimation from P- and L-band SAR imagery is the 
modelling and mitigation of moisture effects [7-11]. An 
uncompensated moisture signal will introduce bias in 
biomass estimates and make them less reliable. Forest 
monitoring is also one of the objectives of the European 
C-band Sentinel-1 SAR systems operating with a center 
frequency of 5405 MHz. It is well-known that C-band 
forest signatures are also affected by moisture variations 
and temporal decorrelation affects repeat-pass 
interferometry [12-14].  Therefore, it is of importance to 
improve the understanding of these effects at P-, L-, and 
C-band. 
 
In tropical forests, moisture effects in a French 
Guianese forest have been investigated during the 
TropiScat campaign [15-16], in which temporal changes 
were studied using a tomographic radar with 20 
antennas mounted on a 55-m high tower. Diurnal cycles 
and rain episodes were observed and it was concluded 
that temporal coherence is highest at dusk and dawn. In 
the AfriScat campaign, a similar experiment is being 
conducted in an African tropical forest in Ghana. 
  
In order to investigate the effects of temporal changes in 
boreal forests on the P-, L-, and C-band signatures, a 
tower-based radar, BorealScat, is being developed by 
Chalmers University of Technology in co-operation 
with the Swedish University of Agricultural Sciences 
(SLU). The test site chosen for the tower radar is 
Remningstorp in southern Sweden which has been used 
for several remote sensing experiments in the past, e.g. 
the BioSAR-1 [17] and BioSAR-3 [18] airborne SAR 
campaigns in 2007 and 2010 funded by ESA.  
 
2. BOREALSCAT 
A dedicated 50-m high tower is currently being 
constructed in the Remningstorp test site. The tower 
will be located at a mature forest stand dominated by 
Norway spruce (Picea abies (L.) Karst.) and which has 
an above-ground dry biomass of 300 tons/ha. Data 
collections are planned to commence in autumn 2016. 
 
The tower radar equipment consists of a 20-channel 
vector network analyser (VNA) from Rhode & Schwarz 
 (ZNBT8, covering 9 kHz-8.5 GHz), an antenna array 
mounted close to the top of the tower, and 20 low-loss 
cables for interconnection as illustrated in Fig. 1. 
External calibration will be performed using a 
permanently installed trihedral corner reflector. An 
internal calibration loop with a switching network (not 
shown in Fig. 1) is also included.  
 
In the first version of BorealScat, the antenna array will 
consist of 20 log-periodic dipole array antennas with 
weather-proof radomes (Rhode & Schwarz HL040E), 
which cover the 0.4-6 GHz frequency range. The 
antennas will be arranged in four vertical columns of 
five antennas, i.e. with separate columns for 
transmission and reception as well as for H- and V-
polarisation as illustrated in Fig. 1. The geometrical 
configuration is similar, but not identical, to that used in 
TropiScat [15-16] and will enable polarimetric, 
tomographic and Doppler measurements at P- and L-
band. Polarimetric and Doppler measurements will also 
be possible at C-band but not tomographic 
measurements due to grating lobes in elevation. In a 
second version of BorealScat, we plan to add a second 
antenna array optimised for C-band tomography.   
 
A dedicated weather station will be installed in close 
proximity of the tower. The system will be connected to 
the internet via a 4G broadband link. A dedicated 
webpage (www.borealscat.se) will also be maintained. 
In situ field measurements and terrestrial lidar scanning 
(TLS) surveys will be conducted by SLU. 
 
 
Figure 1. Conceptual design of BorealScat with the 
principle system blocks, including the tomographic and 
polarimetric array consisting of four columns with five 
wideband log-periodic dipole array elements. 
 
3. CONCLUSIONS 
A tower-based radar facility is being developed and will 
be installed at the Remningstorp forest site. In the first 
version, it will enable polarimetric, tomographic and 
Doppler measurements at P- and L-band. It will be used 
to investigate the effect of changing environmental 
conditions (moisture, wind etc) on the radar data. Data 
collections are planned to commence in autumn 2016. 
Polarimetric and Doppler measurements will also be 
possible up to C-band but not tomography which is 
planned to be added in a future upgrade.  
 
4. REFERENCES 
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Borealscat: A tower experiment for understanding temporal changes in P- and L-band backscattering from a Boreal forest

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