Characterization of bi-direflectance (BRDF) of sea-ice in response to deposited aerosol for the CAL/VAL of remote sensing products.

A project joint with the National Physical Laboratory.

The current understanding of climatic influences of aerosol (such as black carbon) deposited in snow and sea-ice has been described by the intergovernmental panel on climate change, IPCC, to be 'very low'. Volcanic ash, humic material and black carbon deposits in polar snow and sea-ice significantly reduce the reflectivity of the sea-ice or snow. Only nanogram quantities of aerosol per gram of snow are required. 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 prerequisite 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 volcanic ash and humic material will be generated in 2000L tanks. The reflectivity of the sea-ice will be measured in the UV-Vis part of the solar spectrum as a function of zenith and azimuthal angles. The BRDF will be recorded for the sea-ice temperatures of -5 to -20C and ash/humic loadings of 0-100 ng g-1. As part of the work the community will receive a temperature correction to the spectralon reflectance standards used by all reflectance workers.

The project will deliver:
(1) A BRDF as a function of volcanic ash and humic content with an assessment of sensitivity of EO satellites to volcanic ash and humic loading - i.e. can EO satellites be used to measure ash/humic in sea-ice.
(2) A measurement of the spectralon reflectance standard in cold temperatures
(3) Three academic papers reporting the BRDF of seaice as a function of (a) ash surface coverage, (b) humic
concentration, and (c) the temperature correction of spectralon panels to polar temperatures.

The research is low risk, highly rewarding, cost effective and the partnership between Royal Holloway and the National Physical Laboratory. 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 the optics of snow and ice. The project is very exciting and highly relevant since it will improve the understanding of absorbers in snow and ice radiative processes.

The student will have two fantastic learning environments for a very interdisciplinary project directly delivering an important calibration for climate studies by satellites straight to an end user, i.e. clear societal benefit. There is industrial benefit to the UK Earth observing industry, and end-user is the CASE partner so the project has a real pathway to impact.