Laboratory measurements of sea ice: connections to microwave remote sensing

Journal ArticleThe connections between laboratory measurements and remote-sensing observations of sea ice are explored. The focus of this paper is on thin ice, which is more easily simulated in a laboratory environment. We summarize results of C-band scatterometer measurements and discuss how they may help in the interpretation of remote-sensing data. We compare the measurements with observations of thin ice from ERS and airborne radar data sets. We suggest that laboratory backscatter signatures should serve as bounds on the interpretation of remote-sensing data. We examine these bounds from the perspective of thin ice signatures, the effect of temperature, and surface processes, such as frost flowers and slush on these signatures. Controlled experiments also suggest new directions in remote-sensing measurements. The potential of polarimetric radar measurements in the retrieval of thickness of thin ice is discussed. In addition to the radar results, we discuss the importance of low-frequency passive measurements with respect to the thickness of thin ice

Broad spectral, interdisciplinary investigation of the electromagnetic properties of sea ice

Journal ArticleThis paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this Special Section on the Office of Naval Research (ONR), Arlington, VA, Sponsored Sea Ice Electromagnetics Accelerated Research Initiative (ARI)

Electromagnetic Wave Theory and Applications

Contains table of content for Section 3, reports on ten research projects and a list of publications.U.S. Navy - Office of Naval Research Contract N00014-92-J-4098U.S. Federal Aviation Administration Contract 94-G-007U.S. Federal Aviation Administration Contract 97-G-031California Institute of Technology Contract JPL 960408National Aeronautics and Space Administration Contract JPL 958461U.S. Navy - Office of Naval Research Contract N00014-92-J-1616National Science Foundation Grant ECS 96-15799U.S. Navy - Office of Naval Research Contract N00014-97-1-0172Joint Services Electronics Program Contract DAAH04-95-1-0038Mitsubishi Corporatio

Examining the role of sea ice and meteorology in Arctic boundary layer halogen chemistry

Thesis (Ph.D.) University of Alaska Fairbanks, 2015Given the ubiquitous nature of ice, chemistry taking place on ice surfaces has a substantial effect on the environment, particularly in the polar regions. The return of sunlight to the polar regions releases halogen radicals (e.g. Br, Cl and their oxides, e.g. BrO) generated from salts on ice surfaces. These radicals fundamentally alter the chemistry of the Arctic boundary layer through processes such as boundary-layer ozone depletion events and mercury deposition events. Current understanding of the chemical processes involved in Arctic halogen chemistry is inhibited by a lack of knowledge about the ice surfaces on which this chemistry is thought to take place, as well as the sparsity of long-term field observations of this chemistry and its effects. This dissertation addresses both needs through a combination of laboratory experiments and long-term field studies. First, we use X-ray absorption computed micro-tomography at the Advanced Photon Source to image brine distributions within laboratory grown mimics of sea-ice features. These experiments showed that when brine is introduced to ice via wicking of brine from a saline surface, the resulting brine distribution is heterogeneous, with brine existing in distinct regions within the sample, rather than evenly spreading over the sample surface. To examine the horizontal and vertical extent of halogen chemistry in the Arctic boundary layer, we conducted long-term measurements of BrO at Barrow, Alaska using Multiple-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). We developed a method to reduce these measurements to timeseries of near-surface and total column amounts of BrO. These measurements showed that the vertical distribution is highly variable, ranging from shallow layer events confined to the lowest 200 m, to distributed column events, which have lower mixing ratios of BrO, but are more distributed throughout approximately the lowest kilometer of the atmosphere. We find that the observed vertical distributions of BrO are influenced by atmospheric stability. We found minimal influence of wind speed on either lower-tropospheric bromine activation (LT-VCD) or the vertical distribution of BrO, while examination of seasonal trends and the temperature dependence of the vertical distribution support the finding that atmospheric stability affects the distribution of BrO. While shallow layer events have higher concentrations of halogens, distributed column events tend to have higher overall amounts of activation, implying that in situ near surface measurements may be insufficient to constrain the role of environmental parameters in the activation of halogens. Examination of multiple years of data at Barrow, Alaska shows that time spent in first year ice (FYI) areas is weakly linearly correlated (R=0.38) with the activation of BrO. However, examining annual averages of BrO shows that despite the non-linear relationship between time in FYI areas and BrO, time spent in FYI areas still influences the interannual variability of BrO

A broad spectral, interdisciplinary investigation of the electromagnetic properties of sea ice

This paper highlights the interrelationship of research completed by a team of investigators and presented in the several individual papers comprising this Special Section on the Office of Naval Research (ONR), Arlington, VA, Sponsored Sea Ice Electromagnetics Accelerated Research Initiative (ARI). The objectives of the initiative were the following: 1) understand the mechanisms and processes that link the morphological and physical properties of sea ice to its electromagnetic (EM) characteristics; 2) develop and verify predictive models for the interaction of visible, infrared, and microwave radiation with sea ice; 3) develop and verify inverse scattering techniques applicable to problems involving the interaction of EM radiation with sea ice. Guiding principles for the program were that all EM data be taken with concurrent physical property data (salinity, density, roughness, etc.) and that broad spectral data be acquired in as nearly a simultaneous fashion as possible. Over 30 investigators participated in laboratory, field, and modeling studies that spanned the EM spectrum from radio to ultraviolet wavelengths. An interdisciplinary approach that brought together sea ice physicists, remote-sensing experts tin EM measurements), and forward and inverse modelers (primarily mathematicians and EM theorists) was a hallmark of the program. Along with describing results from experiments and modeling efforts, possible paradigms for using broad spectral data in developing algorithms for analyzing remote-sensing data in terms of ice concentration, age, type, and possibly thickness are briefly discussed

The influence of winter time boreal forest tree transmissivity on tree emission and passive microwave snow observations

Forest cover significantly attenuates natural upwelling ground microwave emission from seasonal terrestrial snow. This presents a major challenge for the accurate retrieval of snow from airborne or spaceborne passive microwave (PM) observations. Forest transmissivity is a key parameter describing tree emission because not only does it influence the proportion of sub-canopy upwelling microwave emission penetrating through the forest canopy, it also controls the forest thermal emission. Hence, it is a very important parameter for correcting the influence of forests on spaceborne or airborne observations of the Earth’s land surface. Under sub-zero temperatures, vegetation water content can be frozen influencing the microwave transmissivity of trees. Yet this phenomenon has not been verified through experimentation leaving significant uncertainty in tree emission modelling and spaceborne microwave observations. Therefore, a season-long experiment was designed to study this phenomenon. Ground-based radiometer observations of tree emission, spaceborne observations of forest emission, and model simulations of canopy emission were conducted during this experiment. Based on this experiment, the influence of physical temperature on tree transmissivity was verified, and a model developed to quantitatively describe this temperature-transmissivity relationship. An evaluation of this temperature-transmissivity relationship was conducted showing that both ground-based and spaceborne observations of tree emission are significantly influenced by this phenomenon. Furthermore, passive microwave spaceborne snow retrievals in forested regions are influenced by this phenomenon. Finally, an approach to reduce the influence of the temperature-transmissivity relationship on passive microwave spaceborne snow retrievals is demonstrated

Multi-Sensor Historical Climatology of Satellite-Derived Global Land Surface Moisture

A historical climatology of continuous satellite-derived global land surface soil moisture is being developed. The data consist of surface soil moisture retrievals derived from all available historical and active satellite microwave sensors, including Nimbus-7 Scanning Multichannel Microwave Radiometer, Defense Meteorological Satellites Program Special Sensor Microwave Imager, Tropical Rainfall Measuring Mission Microwave Imager, and Aqua Advanced Microwave Scanning Radiometer for EOS, and span the period from November 1978 through the end of 2007. This new data set is a global product and is consistent in its retrieval approach for the entire period of data record. The moisture retrievals are made with a radiative transfer-based land parameter retrieval model. The various sensors have different technical specifications, including primary wavelength, spatial resolution, and temporal frequency of coverage. These sensor specifications and their effect on the data retrievals are discussed. The model is described in detail, and the quality of the data with respect to the different sensors is discussed as well. Examples of the different sensor retrievals illustrating global patterns are presented. Additional validation studies were performed with large-scale observational soil moisture data sets and are also presented. The data will be made available for use by the general science community

Workshop on the Martian Surface and Atmosphere Through Time

The purpose of the workshop was to bring together the Mars Surface and Atmosphere Through Time (MSATT) Community and interested researchers to begin to explore the interdisciplinary nature of, and to determine the relationships between, various aspects of Mars science that involve the geological and chemical evolution of its surface, the structure and dynamics of its atmosphere, interactions between the surface and atmosphere, and the present and past states of its volatile endowment and climate system

Sea-ice surface properties and their impact on the under-ice light field from remote sensing data and in-situ measurements

The surface properties of sea ice dominate many key processes and drive important feedback mechanisms in the polar oceans of both hemispheres. Examining Arctic and Antarctic sea ice, the distinctly different dominant sea-ice and snow properties in spring and summer are apparent. While Arctic sea ice features a seasonal snow cover with widespread surface ponding in summer, a year-round snow cover and strong surface flooding at the snow/ice interface is observed on Antarctic sea ice. However, substantial knowledge gaps exist about the spatial distribution and temporal evolution of these properties, and their impacts on exchange processes across the atmosphere/ocean interface. This thesis aims to overcome these limitations by quantifying the influence of surface properties on the energy and mass budgets in the ice-covered oceans. Remote sensing data and in-situ observations are combined to derive the seasonal cycle of dominant sea-ice surface characteristics, and their relation to the transfer of solar radiation from the atmosphere through snow and sea ice into the upper ocean. This thesis shows that characteristics of the solar radiation under Arctic sea ice can be described directly as a function of sea-ice surface properties as, e.g., sea-ice type and melt pond coverage. Using this parameterization, an Arctic-wide calculation of solar radiation through sea ice identifies the surface melt onset as the main driver of the annual sea-ice mass and energy budgets. In contrast, an analysis of the spring-summer transition of Antarctic sea ice using passive microwave satellite observations indicates widespread diurnal freeze-thaw cycles in the top snow layers. While the associated temporary thawing is identified as the predominant melt process, subsequent continuous melt in deeper snow layers is rarely found on Antarctic sea ice. Instead of directly influencing the snow depth on Antarctic sea ice, these melt processes rather modify the internal stratigraphy and vertical density structure of the snowpack. An additional analysis of satellite scatterometer observations reveals that snow volume loss on Antarctic sea ice is mainly driven by changes in the lower snowpack, due to the widespread presence of sea-ice surface flooding and snow-ice formation prior to changes in the upper snowpack. As a consequence, the largely heterogeneous and metamorphous Antarctic snowpack prevents a direct correlation between surface properties and the respective characteristics of the penetrating solar radiation under the sea ice. However, surface flooding is identified as the key process governing the variability of the under-ice light regime on small scales. Overall, this thesis highlights that the mass and energy budgets of Antarctic sea ice are determined by processes at the snow/ice interface as well as the temporal evolution of physical snowpack properties. These results are in great contrast to presented studies on Arctic sea ice, where seasonally alternating interactions at the atmosphere/snow- or atmosphere/sea-ice interface control both the energy and mass budgets. An improved understanding of the seasonal cycle of dominant sea-ice and snow surface characteristics in the Arctic and Antarctic is crucial for future investigations retrieving sea-ice variables, such as sea-ice thickness and snow depth, from recent microwave satellite observations

MECA Workshop on Atmospheric H2O Observations of Earth and Mars. Physical Processes, Measurements and Interpretations

The workshop was held to discuss a variety of questions related to the detection and cycling of atmospheric water. Among the questions addressed were: what factors govern the storage and exchange of water between planetary surfaces and atmospheres; what instruments are best suited for the measurement and mapping of atmospheric water; do regolith sources and sinks of water have uniquely identifiable column abundance signatures; what degree of time and spatial resolution in column abundance data is necessary to determine dynamic behavior. Of special importance is the question, does the understanding of how atmospheric water is cycled on Earth provide any insights for the interpretation of Mars atmospheric data