<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE article SYSTEM "http://www.the-cryosphere-discuss.net/inc/tcd/copernicus.dtd">
<article language="en">
	<journal>
		<journal_title>The Cryosphere Discussions</journal_title>
		<journal_url>www.the-cryosphere-discuss.net</journal_url>
		<issn>1994-0432</issn>
		<eissn>1994-0440</eissn>
		<volume_number>2</volume_number>
		<issue_number>5</issue_number>
		<publication_year>2008</publication_year>
	</journal>
	<doi>10.5194/tcd-2-777-2008</doi>
	<article_url>http://www.the-cryosphere-discuss.net/2/777/2008/</article_url>
	<abstract_html>http://www.the-cryosphere-discuss.net/2/777/2008/tcd-2-777-2008.html</abstract_html>
	<fulltext_pdf>http://www.the-cryosphere-discuss.net/2/777/2008/tcd-2-777-2008.pdf</fulltext_pdf>
	<start_page>777</start_page>
	<end_page>810</end_page>
	<publication_date>2008-11-03</publication_date>
	<article_title content_type="html">Comparison of airborne radar altimeter and ground-based Ku-band radar measurements on the ice cap Austfonna, Svalbard</article_title>
	<authors>
		<author numeration="1" affiliations="1">
			<name>O. Brandt</name>
			<email>ola.brandt@npolar.no</email>
		</author>
		<author numeration="2" affiliations="2,5">
			<name>R. L. Hawley</name>
		</author>
		<author numeration="3" affiliations="1">
			<name>J. Kohler</name>
		</author>
		<author numeration="4" affiliations="3">
			<name>J. O. Hagen</name>
		</author>
		<author numeration="5" affiliations="2">
			<name>E. M. Morris</name>
		</author>
		<author numeration="6" affiliations="3">
			<name>T. Dunse</name>
		</author>
		<author numeration="7" affiliations="4">
			<name>J. B. T. Scott</name>
		</author>
		<author numeration="8" affiliations="3">
			<name>T. Eiken</name>
		</author>
	</authors>
	<affiliations>
		<affiliation numeration="1" content_type="html">Norwegian Polar Institute, Tromsø, Norway</affiliation>
		<affiliation numeration="2" content_type="html">Scott Polar Research Institute, Cambridge, UK</affiliation>
		<affiliation numeration="3" content_type="html">University of Oslo, Blindern, Norway</affiliation>
		<affiliation numeration="4" content_type="html">British Antarctic Survey, Cambridge, UK</affiliation>
		<affiliation numeration="5" content_type="html">now at: Dartmouth College, Hanover, NH, USA</affiliation>
	</affiliations>
	<abstract content_type="html">We compare coincident data from the European Space Agency&apos;s Airborne
SAR/Interferometric Radar Altimeter System (ASIRAS) with ground-based Very
High Bandwidth (VHB) stepped-frequency radar measurements in the Ku-band.
The ASIRAS instrument obtained data from ~700 m above the surface,
using a 13.5 GHz center frequency and a 1 GHz bandwidth. The ground-based
VHB radar measurements were acquired using the same center frequency, but
with a variable bandwidth of either 1 or 8 GHz. Four sites were visited with
the VHB radar; two sites within the transition region from superimposed ice
to firn, and two sites in the long-term firn area (wet-snow zone). The
greater bandwidth VHB measurements show that the first peak in the airborne
data is a composite of the return from the surface (i.e. air-snow interface)
and returns of similar or stronger amplitude from reflectors in the upper
~30 cm of the subsurface. The peak position in the airborne data is
thus not necessarily a good proxy for the surface since the maximum and
width of the first return depend on the degree of interference between
surface and subsurface reflectors. The major response from the winter
snowpack was found to be caused by units of thin crust/ice layers (0.5–2 mm)
surrounded by large crystals (&amp;gt;3 mm). In the airborne data, it is possible
to track such layers for tens of kilometers. The winter snowpack lacked
thicker ice layers. The last year&apos;s summer surface, characterized by a low
density large crystal layer overlaying a harder denser layer, gives a strong
radar response, frequently the strongest. The clear relationship observed
between the VHB and ASIRAS waveforms, justifies the use of ground-based
radar measurements in the validation of air- or spaceborne radars.</abstract>
	<references>
		<reference numeration="1" content_type="text"> Alley, R. B., Spencer, M. K., and Anandakrishnan, S.: Ice-sheet mass balance: assessment, attribution and prognosis, Ann. Glaciol., 46, 1–7, 2007. </reference>
		<reference numeration="2" content_type="text"> Arthern, R. J., Wingham, D. J., and Ridout, A. L.: Controls on ERS altimeter measurements over ice sheets: footprint-scale topography, backscatter fluctuations, and the dependence of microwave penetration depth upon satellite orientation, J. Geophys. Res., 106(D24), 471–484, 2001. </reference>
		<reference numeration="3" content_type="text"> Bamber, J., Krabill, W., Raper, V., and Dowdeswell, J.: Anomalous recent growth of part of a large Arctic ice cap: Austfonna, Svalbard, Geophys. Res. Lett., 31, L12402, doi:10.1029/2004GL019667, 2004. </reference>
		<reference numeration="4" content_type="text"> Bevan, S., Luckman, A., Murray, T., Sykes, H., and Kohler, J.: Positive mass balance during the late 20th century on Austfonna, Svalbard, revealed using satellite radar interferometry, Ann. Glaciol., 46, 117–122, 2007. </reference>
		<reference numeration="5" content_type="text"> Brenner, A. C., DiMarzio, J. P., and Zwally, H. J.: Precision and Accuracy of Satellite Radar and Laser Altimeter Data Over the Continental Ice Sheets, IEEE Trans. Geosci. Remote Sens., 45, 2, 321–331, 2007. </reference>
		<reference numeration="6" content_type="text"> Dunse, T., Schuler, T. V., Hagen, J. O., Eiken, T., Brandt, O., and Høgda, K. A.: Recent fluctuations in the extent of the firn area of Austfonna, Svalbard, inferred from GPR, Ann. Glaciol., in press, 2008. </reference>
		<reference numeration="7" content_type="text"> Hamran, S.-E., Gjessing., D. T., Hjelmstad, J., and Aarholt, E.: Ground penetrating synthetic pulse radar: dynamic range and modes of operation, J. Appl. Geophys., 33, 7–14, 1995. </reference>
		<reference numeration="8" content_type="text"> Hawley, R. L., Morris, E. M., Cullen, R., Nixdorf, U., Shepherd, A. P., and Wingham, D. J.: ASIRAS airborne radar resolves internal annual layers in the dry-snow zone of Greenland, Geophys. Res. Lett., 33, L04502, doi:10.1029/2005GL025147, 2006. </reference>
		<reference numeration="9" content_type="text"> Hawley, R. L. and Morris, E. M.: Borehole optical stratigraphy and neutron-scattering density measurements at Summit, Greenland, J. Glaciol., Instruments and Methods, 52, 179, 491–496, 2006. </reference>
		<reference numeration="10" content_type="text"> Hawley, R. L., Brandt, O., Morris, E. M., Kohler, J., Shepherd, A. P., and Wingham, D. J.: Techniques for measuring high-resolution firn density profiles: case study from Kongsvegen, Svalbard, J. Glaciol., Instruments and Methods, 54, 186, 463–468, 2008. </reference>
		<reference numeration="11" content_type="text"> Helm, V., Rack, W., Cullen, R., Nienow, P., Mair, D., Parry, V., and Wingham, D. J.: Winter accumulation in the percolation zone of Greenland measured by airborne radar altimeter, Geophys. Res. Lett., 34, L06501, doi:10.1029/2006GL029185, 2007. </reference>
		<reference numeration="12" content_type="text"> IPCC: Contribution of working group i to the fourth assessment report of the intergovernmental panel on climate change, in: Climate Change 2007: The Physical Science Basis., edited by: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K., Tignor, M., and Miller, H., Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007. </reference>
		<reference numeration="13" content_type="text"> Jezek, K. and Gogineni, S.: Microwave remote sensing on the Greenland ice sheet, IEEE Geoscience and Remote Sensing Society Newsletter, 9, 6–10, 1992. </reference>
		<reference numeration="14" content_type="text"> Jezek, K. C., Gogineni, P., and Shanableh, M.: Radar measurements of melt zones on the Greenland ice sheet, Geophys. Res. Lett., 21, 33–36, 1994. </reference>
		<reference numeration="15" content_type="text"> Kanagaratnam, P., Markus, T., Lytle, V., Heavey, B., Jansen, P., Prescott, G., and Gogineni, S. P.: Ultrawideband Radar Measurements of Thickness of Snow Over Sea Ice, IEEE Trans. Geosci Remote Sens., 45, 9, 2715–2724, 2007. </reference>
		<reference numeration="16" content_type="text"> Kovacs, A., Gow, A. J., and Morey, R. M.: The in situ dielectric constant of polar firn revisited, Cold Reg. Sci. Technol., 23, 3, 245–256, 1995. </reference>
		<reference numeration="17" content_type="text"> Lacroix, P., Legrésy, B., Coleman, R., Dechambre, M., and Rémy, F.: Dual-frequency altimeter signal from Envisat on the Amery ice-shelf, Remote Sens. Environ., 109, 3, 285–294, 2007. </reference>
		<reference numeration="18" content_type="text"> Langley, K., Hamran, S.-E., Høgda, K.-A., Storvold, R., Brandt, O., Hagen, J.-O., and Kohler, J.: Use of C-Band Ground Penetrating Radar to Determine Backscatter Sources Within Glaciers, IEEE Trans. Geosci. Remote Sens., 45, 5, 1236–1246, 2007. </reference>
		<reference numeration="19" content_type="text"> Lentz, H., Braun, H.-M., Younis, M., Fletcher, C., Wiesbeck, W., and Mavrocordatos, C.: Concept and realization of an airborne SAR/ Interferometric Radar Altimeter System (ASIRAS), IGARSS &apos;02, Inst. Electr. Electr. Eng., New York., 6, 3099–3101, 2002. </reference>
		<reference numeration="20" content_type="text"> Morris, E. M.: A theoretical analysis of the neutron scattering method of measuring snow and ice density, J. Geophys. Res., 113, F03019, doi:10.1029/2007JF000962, 2008. </reference>
		<reference numeration="21" content_type="text"> Paterson, W. S. B.: The physics of glaciers. Third Edition. Pergamon, Elsevier Science, Oxford, UK, ISBN 0-08-037944-3, 1994. </reference>
		<reference numeration="22" content_type="text"> Pinglot, J. F., Hagen, J. O., Melvold, K., Eiken, T., and Vincent, C.: A mean net accumulation pattern derived from radioactive layers and radar soundings on Austfonna, Nordaustlandet, Svalbard, J. Glaciol., 47, 159, 555–566, 2001. </reference>
		<reference numeration="23" content_type="text"> Schuler, T. V., Loe, E., Taurisano, A., Eiken, T., Hagen, J.-O., and Kohler, J.: Calibrating a surface mass-balance model for Austfonna ice cap, Svalbard, Ann. Glaciol., 46, 241–248, 2007. </reference>
		<reference numeration="24" content_type="text"> Scott, J. B. T., Nienow, P., Mair, D., Parry, V., Morris, E., and Wingham, D. J.: Importance of seasonal and annual layers in controlling backscatter to radar altimeters across the percolation zone of an ice sheet, Geophys. Res. Lett., 33, L24502, doi:10.1029/2006GL027974, 2006a. </reference>
		<reference numeration="25" content_type="text"> Scott, J. B. T., Mair, D., Nienow, P., Parry, V., and Morris, E.: A ground-based radar backscatter investigation in the percolation zone of the Greenland ice sheet, Remote Sens. Environ., 104, 361–373, 2006b. </reference>
		<reference numeration="26" content_type="text"> Taurisano, A., Schuler, T. V., Hagen, J.-O., Eiken, T., Loe, E., Melvold, K. and Kohler, J.: The distribution of snow accumulation across Austfonna ice cap Svalbard: direct measurements and modeling, Polar Res., 26, 1, 7–13, 2007. </reference>
		<reference numeration="27" content_type="text"> Thomas, R., Frederick, E., Krabill, W., Manizade, S., and Martin, C.: Progressive increase in ice loss from Greenland, Geophys. Res. Lett., 33, L10503, doi:10.1029/2006GL026075, 2006. </reference>
		<reference numeration="28" content_type="text"> Wingham, D. J., Phalippou, L., Mavrocordatos, C., and Wallis, D.: The mean echo and echo cross product from a beamforming interferometric altimeter and their application to elevation measurement, IEEE Trans. Geosci. Remote Sens., 42, 2305–2323, 2004. </reference>
		<reference numeration="29" content_type="text"> Zwally, H. J., Giovinetto, M. B., Li, J., Cornejo, H. G., Beckley, M. A., Brenner, A. C., Saba, J. L., and Yi, D.: Mass changes of the Greenland and Antarctic ice sheets and shelves and contributions to sea-level rise: 1992–2002, J. Glaciol., 51, 175, 509–527, 2005. </reference>
	</references>
</article>

