Characterisation of the bidirectional reflectance distribution function (BRDF) of sea ice in response to deposited black carbon and mineral aerosols. / Lamare, Maxim.

2017. 277 p.

Research output: ThesisDoctoral Thesis

Unpublished

Documents

Abstract

Optical satellite remote sensing is an ideal tool to monitor surface albedo over polar regions, facilitating synoptic observations of expansive areas with a high temporal coverage, which would be unachievable through in situ field measurements. Sea ice does not reflect solar radiation isotropically, therefore the knowledge of the bidirectional distribution function (BRDF) of sea ice is necessary to normalise the data obtained from different sensor viewing angles, and derive surface albedo products. Satellite sensors are limited by a discrete number of viewing angles and spectral bands, and rely on a priori knowledge of the angular distribution of the reflected radiation above the sea ice. Few studies have fully characterised the BRDF of bare sea ice, and the effects of anthropogenic and natural impurities deposited from the atmosphere on the BRDF of sea ice are poorly understood. This study investigates the effects of black carbon and mineral aerosol deposits on the BRDF of sea ice for the calibration and validation of Earth Observation satellite products, based on radiative-transfer modelling, laboratory experiments and field studies. Modelling the impact of different mineral aerosol deposits on the surface albedo of snow and sea ice shows that although mineral light-absorbing impurities significantly change the radiation budget, the type of snow or sea ice has a larger effect than the type of mineral aerosol deposited. The reflectance of a black carbon bearing surface layer of sea ice is recorded in an artificial sea ice laboratory. The reflectance of the doped sea ice is compared to radiative-transfer calculations performed by the TUV-snow radiative-transfer code, in order to validate the model against realistic sea ice conditions. Calculations of downwelling photosynthetically active radiation (PAR) throughout a layer of snow and sea ice help provide an explanation for the observations of an early algae bloom under sea ice in North-East Greenland. PlanarRad, a radiative-transfer model that calculates the angular distribution of radiance, is used to investigate the response of the BRDF of sea ice to varying physical properties. The results highlight the importance of surface roughness, which cannot be considered independently from other parameters. The BRDF of sea ice in response to increasing quantities of black carbon and mineral aerosol deposits in a surface layer are measured in the sea ice laboratory. The results, used to validate PlanarRad, show that the mineral aerosol deposits have a larger effect on the quasi-lambertian part of the hemisphere than on the typical forward scattering peak of the BRDF, however the pattern of the BRDF over the hemisphere does not change. The angular reflectance of bare young sea ice is measured for the first time in an outdoor artificial facility, providing controlled sea ice conditions with natural illumination. Radiative-transfer calculations provided further insight on the optical properties and impurity content of the sea ice. The work presented here provides a better understanding of the BRDF of sea ice, and the impact of atmospheric particulates deposited on the sea ice. Furthermore, the study validates a radiative-transfer model that is of use to the remote sensing community for more accurate satellite retrievals of sea ice.
Original languageEnglish
QualificationPh.D.
Awarding Institution
Supervisors/Advisors
  • King, Martin, Supervisor
  • Fox, Nigel, Supervisor, External person
Thesis sponsors
  • Natural Envt Research Council (NERC)
Award date1 Nov 2017
Publication statusUnpublished - 2017
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 28842947