C11C-01
Using Synthetic Aperture Radar and Lagrangian sea ice tracking to study the seasonal evolution of pack ice thickness and other characteristics
Synthetic Aperture Radars (SARs) respond to the composition and structure of sea ice - which in turn are related to ice age and, indirectly, ice thickness. Examining the evolution of Arctic pack ice characteristics is particularly challenging, since this ice is continuously moving. The traditional Eulerian approach (studying the ice in a particular location) is not effective because ice from different source regions passes through any given study area. This study employed a Lagrangian approach, in which individual parcels of ice were tracked on their journeys through the Arctic. The time series of RADARSAT backscatter from the ice parcels was extracted and then analyzed using a semi-empirical forward simulation model to isolate the factors most responsible for backscatter variability. Results indicate that the backscatter variability of pack ice parcels during the winter and spring is primarily due to incidence angle, the amount of open water within the pack, and the formation and freezing of thin ice in leads. Also revealed in the SAR data are changes in the backscatter of first-year ice as the ice thickens. Changes in the thickness of multiyear ice during winter and spring have little effect on the radar backscatter. The onset of melt in the snow cover causes a precipitous drop in backscatter, after which the amount of liquid water in the snowpack becomes a major source of backscatter variability. Ice that survived summer melt was found to have significantly altered backscatter characteristics in the following winter.
C11C-02
Combined enhanced resolution passive microwave and scatterometer sea ice fields
Passive microwave sea ice concentration fields provide one of the longest running and most consistent records of changes in sea ice. Scatterometer data is a more recently developed product, but now provides several years of sea ice data. Resolution enhancement techniques can provide much higher effective resolution (~10 km) than are available from standard scatterometer and passive microwave fields (25-50 km). Here, we combine sea ice extent fields from enhanced resolution scatterometer data with sea ice concentration fields derived from enhanced resolution passive microwave brightness temperatures to create a merged field that potentially yields higher quality concentration and extent retrievals. The use of multiple sources can yield confidence level estimates that provide pixel-by-pixel insight into the reliability of sea ice fields.
C11C-03
Satellite/Submarine Arctic Sea Ice Remote Sensing in 2004 and 2007
After an interlude of 8 years the U.K. Royal Navy returned to the Arctic Ocean with an under-ice mission by the submarine shape HMS Tireless in April 2004. A full environmental monitoring programme in which U.K. civilian scientists were allowed to participate was integrated into the mission. This was subsequently followed by a second expedition, in March 2007, which allowed further measurements to be acquired. These have so far been the only opportunities for civilian scientists to utilise navy submarines in the Arctic since the demise of the U.S. SCICEX programme in 2000. This paper presents some of the data collected on these new missions and uses it for validation of sea ice information derived from coincident acquisitions by modern satellite sensors such as the ESA Envisat ASAR and NASA MODIS. In both the 2004 and 2007 expeditions shape Tireless took a track north of Greenland along the latitude 85° N. This was similar to the route used for an earlier submarine-aircraft combined survey in April 1987 with which our results shall be compared. In all three missions the submarine was equipped with a standard upward-looking echosounder and sidescan for ice observations and a full range of satellite-borne, or airborne in the case of the earlier mission, microwave and optical sensors were available for validation. In this study we concentrate on the submarine track north of Greenland from the Marginal Ice Zone (MIZ) in Fram Strait through to the Lincoln Sea around 65° W. This transect encompasses a wide range of differing sea ice conditions, from the highly mobile mixture of first year and multi year ice being transported on the trans-polar drift through to the highly deformed ice north of Greenland and Ellesmere Island. The combination of submarine measurements of ice thickness and satellite/aircraft top-side measurements gives an accurate indication of how changes in the ice regime are taking place and allows the potential development of multi-sensor data fusion algorithms for improved sea ice classification and estimation of thickness.
C11C-04
Glacier Changes in the Cordillera Blanca, Peru, Derived From SPOT5 Imagery, GIS and Field- Based Measurements
There is urgency in deriving an extensive dataset for deriving glacier changes within the Cordillera Blanca, Peru, in a cost-effective and timely manner. Rapid glacial retreat during the last decades in this area poses a threat for water resources, hydroelectric power and local traditions. While there is some information on decadal changes in glacier extents, there still remains a paucity of mass balance measurements and glacier parameters such as hypsometry, size distribution and termini elevations. Here we investigate decadal changes in glacier parameters for Cordillera Blanca of Peru using data from Système Probatoire d'Observation de la Terre (SPOT) sensor, an old glacier inventory from 1970 aerial photography, field-based mass balance measurements and meteorological observations. Here we focus on: constructing a geospatial glacier inventory from 2003 SPOT scenes; mass balance estimations using remote sensing and field data; frequency distribution of glacier area; changes in termini elevations; hypsometry changes over time; glacier topography (slope, aspect, length/width ratio); AAR vs. mass balance for Artesonraju and Yanamarey benchmark glaciers; precipitation and temperature trends in the region. Over the last 25 years, mean temperatures increases of 0.09 deg.C/yr were greater at lower elevation than the 0.01 deg.C/yr at higher elevations, with little change in precipitation. Comparison of the new SPOT-based glacier inventory with the 1970 inventory shows that glaciers in Cordillera Blanca retreated at a rate of 0.6% per year over the last three decades, with no significant differences in the rate of area loss between E and W side. At lower elevations there is an upward shift of glacier termini along with a decrease in glacier area. Small glaciers are losing more area than large glaciers. Based on the relationship between specific mass balance (bn) and accumulation area ratio (AAR) for the two benchmark glaciers, we predicted a steady-state equilibrium line altitude (ELA) of approximately 5050 m for the range as a whole. Additional field work is needed to more accurately establish the bn vs. AAR curves and to better determine the most representative benchmark glacier to use in predicting the response of the entire system to climate changes.
C11C-05 INVITED
Mapping East Antarctic Snow Accumulation at High Resolution From Space
Active microwave backscatter measurements from both Radarsat (AMM-1 mapping) and Quikscat show large local variations across the East Antarctic plateau. Comparison of these variations with ground traverse accumulation measurements from ground-penetrating radar and stake measurements shows a consistently high correlation in regions where seasonal melting is absent (generally, in areas >800 m elevation). Backscatter is low in regions of high accumulation and high in regions of lower snowfall. Glaze, or near-zero-accumulation regions have particularly high backscatter. Additional strong correlations are present for local (0.5 km scale) slope in the katabatic wind direction, determined by ICESat and local profiling, and for snow grain size determined from the MODIS Mosaic of Antarctica (MOA) data set. Combined, these data sets show potential for mapping accumulation over large regions of the East Antarctic Plateau at much better resolution (~125-250 m) than presently reported in accumulation compilations. Moreover, the mappings indicate large local variations around surface elevation features. We compare local measurement, the new high-resolution approach to accumulation mapping, and existing recent compiled accumulation data sets over selected regions of the East Antarctic Plateau.
C11C-06
Estimating SWE globally using AMSR-E observations: validation and algorithm development
The Advanced Microwave Scanning Radiometer - EOS (AMSR-E) instrument aboard NASA's Aqua satellite mission is used to estimate daily, five day maximum and monthly average snow water equivalent on a polar projected 25 x 25 km grid. The five-day and monthly products are based on the daily product which uses microwave brightness temperature observations at 10, 18, 36 and 89 GHz, two MODIS land cover products and a snow density "climatology" based on Russian and Canadian data. The current version (B07) of the product implements a dynamic algorithm that has developed from a static approach based on a method by Chang et al. (1987). Retrievals are performed at the native spatial resolution to reflect the measurement "process". This paper describes validation and algorithm developments to the product based on an assessment of the B07 version. New developments to the algorithm that improve the detection capability and that better correct for vegetation are described. The paper also identifies a pathway that will enable the product to reach level 1 validation status.
C11C-07
Radar Observations of Snowpack Changes from the Second Cold Land Processes Experiment
To support the NASA Snow and Cold Land Processes (SCLP) and the ESA Cold Regions High-Resolution Hydrologic Observatory (CoRe-H2O) missions and advance observation of the global water cycle, NASA is supporting the second Cold Land Processes Experiment (CLPX-II). The experiment is being conducted in two parts over two winter seasons (Colorado 2006-2007, and Alaska 2007-2008). The focus of CLPX-II is on testing and development of advanced snow measurement using high-frequency radar through repeat observations of changing snow conditions using airborne and spaceborne radars and intensive in situ measurements. During 2006-2007 three field campaigns were conducted in a 90-km x 9-km study area in north-central Colorado. The campaigns were carried out in December, January and February to observe significant changes in snowpack characteristics. In each campaign, the Jet Propulsion Laboratory's conically scanning Ku- band polarimetric scatterometer (POLSCAT) was flown on a Twin Otter aircraft to collect radar data over the study area. Multiple complete images of the entire study area were acquired during each campaign, enabling examination of short-term changes in radar response as well as long-term changes between campaigns. In each campaign, intensive in situ observations of snow depth, water equivalent, stratigraphy, and grain size were made in each of 16 target sites. All of the target sites shared similar backgrounds (flat terrain with a ground cover of grasses and sedges) but exhibited a wide range of snowpack characteristics. Preliminary analyses of the POLSCAT data acquired from the CLPX-II in winter 2006-2007 are described. The data showed response of the Ku-band radar echoes to snowpack changes for various types of background vegetation. There was about 0.4 dB increase in backscatter for every 1 cm SWE accumulation for sage brush and pasture fields. The data also showed the impact of freeze/thaw cycles, which appeared to create depth hoar and ice lenses with large snow grain size, and consequently increased the radar signals by a few dBs.
C11C-08
An Improved Northern Hemisphere Snow Extent Data Record
It has been 40 years since satellite-derived maps of Northern Hemisphere snow cover extent (SCE) began being produced by National Oceanic and Atmospheric Administration meteorologists. No other environmental variable has been mapped from satellite data in a generally consistent manner for such a long period. Information generated from these maps has been used in international assessments of climate variability and change, and in numerous investigations regarding the role of snow cover in the climate system. Despite their proven climate utility, meteorological forecasting has long been the driving force behind producing these maps. As such, changes (documented and undocumented) in mapping methodologies have occurred over time, without a focus on their climatological continuity. In particular, 1999 brought a change from weekly to daily maps and a greatly increased resolution to the map's digitized grid. Members of our Global Snow Lab, as well as others elsewhere, have kept a watchful eye on changes in this satellite environmental data record (EDR). We saw the need to thoroughly scrutinize the EDR and to develop a satellite SCE climate data record (CDR). This presentation will discuss efforts within the Global Snow Lab to do just that, and will introduce this CDR. Comparisons of climatologies and time series between the new CDR and the past EDR will be presented, along with estimates of CDR error limits. Updated time series analyses of regional to hemispheric SCE through this past fall will also be discussed, along with efforts underway that will integrate visible and microwave satellite and station-observed estimates of extent and depth into valuable new CDRs. http://climate.rutgers.edu/snowcover