• 16:30 The BIOMASS Mission: Secondary Objectives

  Paillou, Philippe (1); Dall, Jorgen (2); Scipal, Klaus (3) 1: University of Bordeaux, France; 2: Technical University of Denmark; 3: European Space Agency, ESTEC

  Show abstract

  The BIOMASS mission was selected in 2013 by the European Space Agency as the 7th ESA Earth Explorer Mission. It is aimed at a global mapping of the continental biomass, to support reporting on carbon stocks and models. The instrument foreseen for the BIOMASS mission is a P-band SAR (435 MHz central frequency, 6 MHz bandwidth), with full polarimetric capabilities. The orbit is near polar, sun-synchronous at an altitude around 660 km, and will enable repeat-pass interferometry with a repeat cycle not exceeding 17 days. The mission is planned to be launched in 2020 and to last five years, and a global coverage of continental surfaces will be achieved in six months. Besides the main objective of mapping the continental biomass, the P-band SAR of BIOMASS shall also be considered for secondary objectives, exploiting the unique long-wavelength properties of a P-band imaging radar. No such space-borne low frequency SAR exists yet, but airborne experiments have shown that P-band has high potential for applications such as sub-surface geology mapping, ice sounding, topography mapping, soil moisture monitoring and inundation mapping. We shall describe plans of the BIOMASS mission for three main secondary applications which are considered as “ready-to-fly”: mapping sub-surface geology, ice flow measurement, and digital elevation model generation.

  
   

• 16:50 A Comparison of L- and P-band PolSAR Observations of a Sub-polar Ice-cap

  Parrella, Giuseppe (1,2); Hajnsek, Irena (1,2); Papathanassiou, Konstantinos (1) 1: German Aerospace Center (DLR), Microwave and Radar Institute, Wessling (DE); 2: ETH Zurich, Institute of Environmental Engineering, Zurich (CH)

  Show abstract

  Polarimetric SAR observations at long-wavelengths (e.g. L- and P- band) provide the possibility to characterize the near-surface structure of glaciers and ice sheets. The knowledge of such information is crucial for understanding and monitoring the dynamic of ice masses [1]. With dry snow conditions, SAR signal penetrates several meters through snow and ice, interacting with buried features, like ice lenses, air bubbles, etc. The structure of subsurface layers determines the penetration depth of the SAR waves. In a polarimetric SAR (PolSAR) sensor, the penetration capability of microwaves is combined to the additional information brought by the polarization diversity, which provides high sensitivity to scatterers properties [2]. This paper addresses the interpretation of L- and P- band PolSAR measurements over the Austfonna ice-cap, Svalbard, by using the polarimetric scattering model presented in [3]. In detail, two test sites are investigated, which are located in different glacier zones [4] of the ice-cap. Experimental SAR data were collected by the airborne E-SAR sensor of the German Aerospace Center at L- (1.3 GHz) and P-band (0.35 GHz) over the percolation zone and the superimposed ice region of Austfonna, in spring 2007 during the ICESAR campaign. First, a qualitative polarimetric data analysis is performed based on a set of descriptors which includes backscattering coefficients, co-polarization ratio, co-polarization phase difference, entropy and mean alpha angle. Differences appearing between the two sites at both frequencies are discussed and related to the differences in subsurface structure with the support of ground measurements. A polarimetric decomposition, based on the scattering models proposed in [3], is also applied to the SAR data to provide a quantitative estimation of physical parameters at both locations. A final discussion addresses the incongruences observed by comparing the results obtained at L- and P-band over each site. The difference in wavelength turns out to generate significant changes in the observed scattering properties, suggesting that the adopted scattering model fits better the L-band case. In fact, one of the assumptions made in [3] is that only single scattering occurs in order to consider the different scattering components uncorrelated. At P-band, this hypothesis might not hold as the radar wavelength is about 86cm and the scatterers might be not sparse enough to avoid multiple interactions, even in the case of the percolation zone where very few ice lenses and pipes per square meter are expected [4]. Furthermore, additional scattering mechanisms generated in deeper layers, which are not sensed at L-band, might significantly contribute to the total P-band backscattering. REFERENCES [1] W.S.B. Paterson, The Physics of Glaciers, 3rd ed. Oxford, U.K.: Pergamon Press, 1994. [2] S. Cloude, Polarisation: Application in Remote Sensing. London, U.K.: Oxford Univ. Press, 2010. [3] G. Parrella, I. Hajnsek and K. Papathanassiou, “On the interpretation of L- and P- band PolSAR signatures of polythermal glaciers”, in Proc. of 6th International Workshop on Science and Applications of SAR Polarimetry and Polarimetric Interferometry (PolinSAR), Frascati, Italy, 2013. [4] C.S. Benson, “Stratigraphic studies in the snow and firn of the Greenland ice sheet”, Ph.D. dissertation, California Institute of Technology, Pasadena, California, 1960.

  
   

• 17:10 The effect of dielectric changes on ice velocities measured with polarimetric DInSAR

  Dall, Jørgen; Nielsen, Ulrik; Kusk, Anders Technical University of Denmark, Denmark

  Show abstract

  The velocity field of glaciers and ice sheets can be mapped with multi-temporal SAR. Offset tracking and differential interferometry (DInSAR) are the two classes of techniques used. DInSAR includes the double difference algorithm and the DEM elimination algorithm. In this study, DEM elimination is applied, i.e. an external digital elevation model (DEM) is used to eliminate the interferometric phase contributed by the surface topography in combination with a spatial baseline. In this way the phase that is proportional to the ice displacement is ideally isolated. A phase artifact has previously been observed in L-band ice data [1]. The artifact adds to the topography and displacement phases thereby causing velocity errors. Presumably, the phase artifact is caused by a dielectric change of the ice occurring between the two data acquisitions. This change is visible when comparing HH and VV polarized interferograms [1], and the artifact might be larger at P-band than at L-band because the penetration depth is larger at P-band than at L-band. The Biomass Earth Explorer mission is a fully polarimetric P-band SAR, and the secondary objectives suggested for Biomass include velocity and structure of glaciers and ice sheets. Extrapolation from higher frequencies suggests less temporal decorrelation at P-band. The larger penetration depth at P-band means less temporal decorrelation, as the influence of near-surface change processes reduces with increasing penetration depth. A high correlation is crucial to DInSAR and to the offset tracking variant known as speckle tracking. ESA’s IceSAR 2012 campaign was carried out in support of the Biomass mission, and it made use of POLARIS, an airborne polarimetric P-band SAR, developed for ESA by the Technical University of Denmark. POLARIS was originally an advanced ice sounding radar [2], but prior to the IceSAR campaign a SAR capability was added by enabling the antenna beam to be directed to the side. The IceSAR flights in Greenland in June 2012 were preceded by three flights over the Langjökull ice cap in Iceland. Fully polarimetric data were acquired, and the flight tracks were defined with nominally zero baseline in order to ensure maximum coherence and minimum sensitivity to topography. Penetration into ice can cause a significant interferometric phase change [3], [4]. By beginning the data acquisitions at 4 AM and 4 PM one day and again at 4 AM the following day, the difference in ice temperature (and possibly in liquid water content) can be maximized, thereby ensuring the largest possible dielectric change and hence the largest phase artifact. The flights over the Langjökull were coordinated with a series of L-band data acquisitions with the JPL UAVSAR in a projected led by Caltech [1]. One of the primary goals was to analyse the capabilities and limitations of DInSAR ice velocity measurements. Prior to the campaign, Caltech deployed ten phase differential GPS receivers on (and north of) Vestari Hagafellsjökull, one of the outlet glaciers of Langjökull. The GPS data provide accurate displacement information for validation. The POLARIS data have been focused with the back-projection algorithm and directly mapped onto a DEM provided by the University of Iceland [5]. This ensures easy and precise motion compensation and coregistration. After DEM elimination only the ice displacement and a potential phase artifact contribute to the interferometric phase. Since the temporal baselines of the POLARIS flights do not exceed 12–24 hours, the ice displacement is just a few centimeters. In addition, both the ice displacement and a potential residual topographic contribution have the same effect at all polarizations, so the topography and displacement phases do not impact the difference between the HH and VV interferograms, unlike the phase artifact, which is supposed to vary with the polarization because the combination of volume scattering and surface scattering implies a polarization dependency. The phase artifact is also supposed to depend on the temporal baseline, i.e. it is large for a 12 hours baseline and small for a 24 hours baseline. The outcome of this analysis will be presented. [1] M. Simons, Caltech, Personal Communication, March 2012. [2] J. Dall, S.S. Kristensen, V. Krozer, C.C. Hernández, J. Vidkjær, A. Kusk, J. Balling, N. Skou, S.S. Søbjærg, E.L. Christensen, “ESA’s polarimetric airborne radar ice sounder (POLARIS): Design and first results”, IET Radar, Sonar & Navigation, Vol. 4, No. 3, pp. 488-496, June 2010. [3] J. Dall, S.N. Madsen, K. Keller, R. Forsberg, “Topography and Penetration of the Greenland Ice Sheet Measured with Airborne SAR Interferometry”, Geophysical Research Letters, Vol. 28, No 9, pp. 1703-1706, May 2001. [4] J. Dall, “InSAR elevation bias caused by penetration into uniform volumes”, IEEE Transactions on Geoscience and Remote Sensing, Vol. 45, No. 7, pp. 2319-2324, July 2007. [5] F. Pálsson, University of Iceland, Personal Communication, 2013.

  
   

• 17:30 Round Table Discussion

  Show abstract

  Round Table Discussion

  
   

Highlights

In May 2013, the Biomass mission concept was selected to become the next in the series of satellites developed to further our understanding of Earth.

Released: 21/06/2013

REPLAY EARTH EXPLORER 7 USER CONSULTATION MEETING (PART 1)

Released: 11/03/2013

POLinSAR 2013 Workshop

Released: 22/02/2013