Measurement of bi-direflectance (BRDF) of sea-ice for Earth Observing Satellites

Lead Research Organisation: Royal Holloway, University of London
Department Name: Earth Sciences

Abstract

The current understanding of climatic influences of black carbon in snow and sea-ice has been described by the intergovernmental panel on climate change, IPCC, to be 'very low' and a better examination of these processes is clearly required. Black carbon from increasing anthropogenic (and biogenic) combustion deposits in polar snow and sea-ice to significantly reduce the reflectivity of the sea-ice or snow. The reduced reflectivity of the Earth surface results in increased warming of the planet. Satellite observations allow for the synoptic observation of large areas of the globe. Remote sensing observations performed in the visible and near infrared (e.g. Meris, MODIS, AVHHR) have wide application in marine, land and snow/ice related climate studies serving as both primary and secondary sources of information. However, although there is significant value in the analysis of data from individual sensors, any global observing system and in particular studies requiring different spatial resolutions and long time bases require accurate knowledge of sensor to sensor biases. This requires the responsivities of all optical radiometers operated in space to be intercompared and traceable to a common reference standard. CEOS (Committee on Earth Observing Satellites) has established a number of Earth targets to serve as international reference standards, each being, or to be, well characterized by surface based in-situ measurements. The reflectance of natural surfaces is not isotropic. The reflectance varies with the illumination and viewing geometries, and consequently impacts satellite observations. Thus the bi-directional reflectance (BRDF) of natural surfaces is a pre-requisite for use of satellite data. Sea-ice is a strong potential calibration target. Working closely with both supervisors the PhD student will generate sea ice in the new RHUL sea-ice simulator. Sea-ice doped with different concentrations of black carbon will be generated in 2000L tanks. The reflectivity of the sea-ice will be measured in the UV and visible parts of the solar spectrum with different zenith and azimuthal angles. The BRDF will be recorded for the sea-ice temperatures of -5 to -25C and black carbon loading of 0-100 ng g(-1). The project will deliver:- (1) A BRDF for sea-ice that can be used by Earth observing satellites to inter-calibrate. This will be delivered to the end users by CASE partner - Dr Nigel Fox, NPL. (2) A BRDF as a function of black carbon content with an assessment of sensitivity of EO satellites to Black carbon loading - i.e. can EO satellites be used to measure BC in sea-ice. (3) Three academic papers reporting the BRDF of seaice as a function of (a) temperature, (b) black carbon concentration, and (c) the sensitivity of BRDF to size, shape, refractive index of the black carbon. The proposed research is low risk, highly rewarding and cost effective and the partnership between Royal Holloway and the NPL is an excellent training opportunity for a PhD student. The applicants have demonstrated in preliminary studies that all experiments are feasible, and have complimentary extensive experience in making BRDF measurements for satellite calibration and measuring the optics of snow and ice. The project is very exciting and highly relevant since it will improve the understanding of black carbon in snow and ice radiative processes. The financial resources required are minimal, RHUL has constructed the sea-ice simulator with CIF money and supported it with a PhD studentship to study ice biogeochemistry. The student will have two fantastic learning environments for this very interdisciplinary project that will directly deliver an important calibration for climate studies by earth observing satellites straight to an end user - i.e. there is clear societal benefit. There is industrial benefit to the UK satellite and Earth observing industry, and end-user is the CASE partner so the project has a real pathway to impact.

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