Principal Investigator (PI): Ronald Kwok, NASA's Jet Propulsion Laboratory
To date, RADARSAT-1 has provided over twelve years (1997-2008) of near-uninterrupted 3-day mappings of that portion of the Arctic Ocean ice cover within the Alaska Satellite FacilityDistributed Active Archive Center (ASF DAAC) reception mask. The multi-year Earth System Data Records (ESDRs) of high-resolution sea ice kinematics and deformation derived from this time-series of synthetic aperture radar (SAR) observations, developed under the current NASA Making Earth System Data Records for Use in Research Environments (MEAsUREs) project, have contributed to the understanding of the sea ice cover. This included: the development of new approaches for modeling the mechanical behavior of sea ice and the validation of these models; the characterization of the sub-daily ice motion; a description of the seasonal and regional variability of sea ice deformation; validation of Ice, Cloud,and land Elevation Satellite (ICESat) freeboard algorithms; and, the estimates of sea ice exchange between the Arctic Ocean and its peripheral seas.
The SAR data stream from RADARSAT-1 terminated in mid-2008 with the expiration of the Memorandum of Understanding of data exchange between Canadian Space Agency and NASA. As a consequence, we lost the reliable and routine RS-1 acquisitions over the Arctic Ocean. Potentially, the SAR data stream from European Space Agency environmental satellite (Envisat) is a substitute for RS-1. However, even though the Envisat SAR offers the same wide-swath imaging mode as RS-1 for large-scale mapping, the Envisat radar has not been tasked to provide the same Arctic coverage as RS-1. Due to mission constraints, the ESA radar has focused on that part of the Arctic that has not been routinely covered by RS-1.
Since April 2007, the Envisat acquisitions have provided high-density coverage of the Arctic Ocean poleward of 80°N inside of 130°E and 40°W. This coverage included: the Fram and Nares Straits - the two passages where the largest fraction of sea ice export has been recorded; and, the area of the Arctic Ocean north of Greenland and Ellesmere Island that contained the largest fraction of thick, old, multiyear sea ice. Climatologically, these regions are especially interesting with respect to the loss of perennial ice coverage and the mass balance of the Arctic Ocean.
Furthermore, the Envisat acquisitions have been providing higher density temporal sampling (compared to RS-1) of an area of ice north of Greenland that could be useful for understanding sub-daily ice motion and deformation. At these latitudes where many orbits converge, the wide-swath SAR coverage provides 4–5 sequential observations every day, for ice motion retrieval, with a sampling interval at the orbital period of ~101 minutes. Preliminary investigations, using data from a brief RS-1 campaign in 2002, show sub-daily deformations that are more likely associated with inertial rather than tidal frequencies. These observations are remarkable in that short-period ice motion is previously believed to be inhibited by the strength of the ice pack in the high Arctic during winter.
The limited RS-1 data showed new ice production due to the recurrent openings and closings at these temporal scales. If ubiquitous, as the ice cover gets weaker, it could be a significant source of ice production within the winter pack. The Envisat data will allow a more extensive monitoring of this process of ice production during all seasons, as this process may become climatologically important as the ice cover thins and weakens. Additionally, the data set provides a rare opportunity to provide the first systematic look at the small-scale behavior of the ice cover with a unified ESDR. From this data set, we propose to a produce a coherent set of observations of sea ice motion of the Arctic and Southern Oceans.
We will also address the utility of Sentinel-1 for producing ESDR of ice motion of the Arctic Ocean. ESA’s Sentinel-1, planned for launch in 2013 time frame, is expected to provide routine coverage of not only the Arctic Ocean but also the Southern Ocean. If this operational plan is realized, this will be a significant data set that could contribute to the ESDR of the polar oceans. Thus, understanding the mission plans and the data distribution issues are important in the immediate post-launch time frame. We propose:
- to process the Envisat data stream to construct a record of small-scale ice motion of the Arctic Ocean;
- to develop products that take advantage of the temporal and spatial sampling scheme of the Envisat mission;
- to produce mosaics of the Envisat images of the Arctic Ocean;
- to create a multi-year time series of Fram Strait and Nares Strait sea ice export; and,
- to address the use of Sentinel-1 data sets for producing ESDR of the Arctic and Antarctic ice cover.
The image mosaics are new products that will support a wide variety of research topics and comparison with historical SAR datasets from ERS-1, ERS-2, and RS-1. These datasets will add to the publicly available archive of RADARSAT image and ice motion products.