ACS  Vol.4 No.5 , December 2014
Improved Retrieval of Sea Ice Thickness and Density from Laser Altimeter
Author(s) Vera Djepa*
The sensitivity of weather and climate system to sea ice thickness (SIT) in the Arctic is recognised from various studies. Decrease of SIT will affect atmospheric circulation, temperature, precipitation and wind speed in the Arctic and remotely. Ice thermodynamics and dynamic properties depend strongly on ice and snow thickness. The heat transfer through ice critically depends on ice thickness. Long term accurate SIT records with corresponding uncertainties are required for improved seasonal weather forecast and estimate of the sea ice mass balance. Satellite radar and Laser Altimeter (LA) provide long term records of sea ice freeboard. Assuming isostatic equilibrium, SIT is retrieved from the freeboard, extracted from radar altimeter (RA) or LA, where the snow depth, density, ice and water density are input variables in the equation for hydrostatic equilibrium to derive SIT from LA or RA. Different input variables (snow depth, density, ice and water density) with unknown accuracy have been applied from various authors to retrieve SIT and Sea Ice Draft (SID) from RA or LA, leading to not comparative results. Sea ice density dependence on ice type, thermodynamic properties and freeboard is confirmed with different studies. Sensitivity analyses confirm the great impact of sea ice density, snow depth and density on accuracy of the retrieved SIT and the importance of inserting variable ice density (VID) in the equation for hydrostatic equilibrium for more accurate SIT retrieval, weather and climate forecast. The impact of sea ice density and snow depth and density on retrieved SIT from the freeboard derived from LA and RA have been analyzed in this study using the equation for hydrostatic equilibrium, statistical and sensitivity analyses. An algorithm is developed to convert the freeboard, derived from LA in SIT, inserting VID in the equation for hydrostatic equilibrium. The algorithm is validated with field, laboratory studies and collocated SIT retrieved from RA on board Envisat. The accuracy of the developed algorithm is analyzed, using statistical and uncertainty analyses. It is found that the uncertainty of the retrieved SIT from LA is decreased 7.6 times (from rhi = 59 cm for fixed ice density) if variable ice density is inserted in the equation for hydrostatic equilibrium. The SIT, which has been retrieved from the freeboard derived from LA is validated with collocated SIT derived from RA2 on Envisat, using variable ice density. The bias of the mean SIT derived from LA and RA has been reduced from -1.1 m to about one millimeter when VID is applied to retrieve SIT from LA and RA. The results and algorithms, discussed in this paper are essential contribution to SIT and SID retrieval, satellite remote sensing, cryosphere, meteorology and improved weather and climate forecast.

Cite this paper
Djepa, V. (2014) Improved Retrieval of Sea Ice Thickness and Density from Laser Altimeter. Atmospheric and Climate Sciences, 4, 907-918. doi: 10.4236/acs.2014.45080.
[1]   Cheng, B., Mäkynen, M., Similä, M., Rontu, L. and Vihma, T. (2013) Modelling Snow and Ice Thickness in the Coastal Kara Sea, Russian Arctic. Annals of Glaciology, 54, 105-113.

[2]   Stroeve, J., Holland, M.M., Meier, W., Scambos, T. and Serreze, M. (2007) Arctic Sea Ice Decline: Faster than Forecast. Geophysical Research Letters, 34, Article ID: L09501.

[3]   Screen, J.A. and Simmonds, I. (2013) Exploring Links between Arctic Amplification and Mid-Latitude Weather. Geophysical Research Letters, 40, 959-964.

[4]   Petoukhov, V. and Semenov, V.A. (2010) A Link between Reduced Barents-Kara Sea Ice and Cold Winter Extremes over Northern Continents. Journal of Geophysical Research, 115, Article ID: D21111.

[5]   Kurtz, N.T., Farrell, S.L., Studinger, M., Galin, N., Harbeck, J., Lindsay, R., Onana, V., Panzer, B. and Sonntag, J.G. (2012) Sea Ice Thickness, Freeboard, and Snow Depth Products from Operation Ice Bridge Airborne Data. Cryosphere Discussions, 6, 4771-4827.

[6]   Kwok, R. (2010) Satellite Remote Sensing of Sea Ice Thickness and Kinematics a Review. Journal of Glaciology, 56, 1129-1140.

[7]   Kwok, R., Cunningham, G.F., Wensnahan, M., Rigor, I. and Zwally, H.J. (2008) Thinning and Volume Loss of the Arctic Ocean Sea Ice Cover: 2003-2008. Journal of Geophysical Research, 114, Article ID: C07005.

[8]   Connor, L., Seymour, W., Laxon, B., Ridout, A.L., Krabill, W.B. and McAdoo, D.C. (2009) Comparison of Envisat Radar and Airborne Laser Altimeter Measurements over Arctic Sea Ice. Remote Sensing of Environment, 113, 563-570.

[9]   (2013) Algorithm Theoretical Basis Document SICCI-ATBD.

[10]   Warren, S. and Rigor, I. (1999) Snow Depth on Arctic Sea Ice. Journal of Climate, 12, 1814-1829.

[11]   Laxon, S., Giles, K.A., Ridout, A.L., Wingham, D.J., Willatt, R., Cullen, R., Kwok, R., Schweiger, A., Zhang, J., Haas, C., Hendricks, S., Krishfield, R., Kurtz, N., Farrell, S. and Davidson, M. (2013) CryoSat-2 Estimates of Arctic Sea Ice Thickness and Volume. Geophysical Research Letters, 40, 1-6.

[12]   Djepa, V. (2014) Sensitivity Analyses of Sea Ice Thickness Retrieval from Radar Altimeter. Journal of Surveying and Mapping Engineering (JSME), 2, 44-55.

[13]   Hallikainen, M. (1992) Review of the Microwave Dielectric and Extinction Properties of Sea Ice and Snow. Geosciences and Remote Sensing Symposium, IGARSS 92, 2, 961-965.

[14]   Kovacs, A. (1996) Sea Ice. Estimating the Full Scale Tensile, Flexural and Compressive Strength. CRREL (Cold Regions Research and Engineering Laboratory) Report 96-11, Hanover, New Hampshire 03755-1290, USA.

[15]   Ackley, S.F., Hibler III, W.D., Kugzruk, F., Kovacs, A. and Weeks, W.F. (1976) Thickness and Roughness Variations of Arctic Multiyear Sea Ice. CRREL (Cold Regions Research and Engineering Laboratory) Report 76-18, 24 p, Hanover, New Hampshire 03755-1290, USA.

[16]   Alexandrov, V., Sandven, S., Wahlin, J. and Johannessen, O.M. (2010) The Relation between Sea Ice Thickness and Freeboard in the Arctic. The Cryosphere Discussion, 4, 373-380.

[17]   NSIDC (National Snow and Ice Data Centre) (2014).

[18]   Farrell, S.L., Kurtz, N.T., Connor, L., Elder, B., Leuschen, C., Markus, T., McAdoo, D.C., Panzer, B., Richter-Menge, J. and Sonntag, J. (2012) A First Assessment of Ice Bridge Snow and Ice Thickness Data over Arctic Sea Ice. IEEE Transactions on Geoscience and Remote Sensing, 50, 2098-2111.

[19]   Wadhams, P., Tucker, W.B., Krabill, W.B., Swift, R.N., Comiso, J.C. and Davis, R.N. (1992) Relationship between Sea Ice Free Board and Draft in the Arctic Basin, and Implication for Ice Thickness Monitoring. Journal of Geophysical Research, 97, 20325-20334.

[20]   Cavalieri, D.J., Markus, T., Ivanof, A., Miller, J.A., Brucker, L., Sturm, M., Maslanik, J., Heinrichs, J.F., Gasiewski, A.J., Leuschen, C., Krabill, W. and Sonntag, J. (2012) A Comparison of Snow Depth on Sea Ice Retrievals Using Airborne Altimeters and AMSR-E Simulator. Geoscience and Remote Sensing, 50, 3027-3039.

[21]   Worby, A.P., Markus, T., Steer, A.D., Lytle, V.I. and Massom, R.A. (2008) Evaluation of AMSR-E Snow Depth Product over East Antarctic Sea Ice Using in Situ Measurements and Aerial Photography. Journal of Geophysical Research, 113, Article ID: C05S94.