Support to Multi-Frequency Microwave Scatterometer measurements during MOSAiC

High-resolution measurements of multi-frequency scatterometer data were collected during the year-long MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) International Arctic Drift Expedition in the Central Arctic between October 2019 and October 2020.

The MOSAiC expedition provided the unique and unprecedented opportunity to obtain and interpret a benchmark dataset involving in-situ and satellite measurements of Ka-, Ku-, X-, C- and L-band microwave data and fiducial reference measurements of snow and sea ice physical properties over a complete annual cycle. These data will be further used towards the development and validation of satellite-based retrieval algorithms, as well as the improvement of microwave radiative transfer models.

Such an extensive dataset has not been available to date.

The MOSAiC multi-frequency scatterometer campaign was a success and the acquired data are of high quality. These datasets are crucial towards process-scale understanding and interpretation of microwave interactions of snow and sea ice, in turn aiding accurate retrievals of snow and sea ice critical state variables, such as freeze-up and melt-onset timings, snow depth, and sea ice thickness retrievals from present and forthcoming spaceborne scatterometer instruments, such as the Advanced SCATterometer (ASCAT) and the Scatterometer (SCA) as well as Synthetic Aperture Radars (SAR) missions, such as TerraSAR-X, Sentinel-1, RCM, ALOS-2 PALSAR-2, and ROSE-L.

Remote sensing instruments in the Central Observatory

Objectives

The scatterometer measurements were being acquired to investigate the temporal evolution of signals caused by by meteorological and geophysical changes such as:

• snow accumulation and metamorphism;
• temperature changes;
• ice growth and melting;
• desalination;
• ice crusts and wind-packed snow formation, etc.

These changes are effective on a satellite footprint scale, which will allow comparison to the temporal evolution of the ground-based and satellite scatterometer/radar measurements.

In particular, for the first time, it became possible to evaluate and quantify the seasonal evolution of snow cover on younger and thinner first-year sea ice (greater than a few cm) through to older and thicker multi-year sea ice. With these in-situ microwave scatterometer measurements, we will now be able to better understand the electromagnetic interaction with seasonally-evolving snow and sea-ice, and, thus, the signal measured by radar satellites. This will, in turn, help to modify and refine retrieval methods of snow and ice properties from these measurements and and improve forward models of the radiative transfer in the snow and sea ice. MOSAiC offered the unique opportunity to collect these joint measurements under different environmental conditions, starting with the ice freeze-up and first snow accumulation throughout the winter (Legs 1 to 3 between October 2019 and May 2020) until spring and summer (Legs 4 and 5 between June and October 2020), when the snow and sea ice start to melt and strong radiometric changes occur. Campaigns such as MOSAiC are critical and essential for us to timely improve and monitor a rapidly evolving sea ice regime from satellites under warming Arctic conditions.

Overview

Sea ice is an integral part of the global climate system, the marine ecosystem and traditional ways of living in northern communities, but also an obstacle for the shipping and offshore industry. To obtain hemispheric-scale information about sea ice and the snow cover on top, satellite remote sensing is the method of choice. Microwave frequencies are ideally suited to observe sea ice/snow because they are largely independent of clouds and penetrate the snow and sea ice.

The MOSAiC team, led by Team ICE, deployed a suite ground-based multi-frequency scatterometers (systems operating at Ka-, Ku-, X- and L-band frequencies). The systems were deployed at the remote sensing site on the MOSAiC floe and the scatterometer observations were complemented by coincident and detailed in-situ measurements of snow and sea ice properties collected weekly from the remote sensing site, and microwave radiometer measurements (P-, L-, C-, X-, K- and Ka-band).

Observations collected during the MOSAiC campaign will help us better interpret the measurements of current and future EUMETSAT/ESA/EU Copernicus satellite missions, validated with in-situ observations of microwave measurements, meteorological observations and snow/sea ice geophysical property data. Furthermore, microwave radiative transfer (MRT) models of snow and sea ice will be improved using coincident observations of snow/sea ice physical properties, along with scatterometer measurements. MRT models are required for the retrieval of sea ice and snow properties (e.g. ice thickness and snow depth on sea ice) from satellite missions such as Sentinel-3 and EPS-SG and forthcoming missions such as ESA’s CRISTAL.

Detailed information on the outcomes of this activity can be found in STUDY DOCUMENTS section below.