|Paper title||Simulations of improved glint observations over snow for CO2M|
|Form of presentation||Poster|
The Arctic and boreal regions have unique and poorly understood natural carbon cycles as well as increasing anthropogenic activities, e.g. from the oil and gas industry sector. The evolution of the high-latitude carbon sources and sinks would be most comprehensively observed by satelllites, in particular the planned Copernicus Anthropogenic CO2 Monitoring mission (CO2M). However, high latitudes pose significant challenges to reliable space-based observations of greenhouse gases. In addition to large solar zenith angles and frequent cloud coverage, snow-covered surfaces absorb strongly in the near-infrared wavelengths. Because of the resulting low radiances of the reflection measured by the satellite in nadir geometry, the retrievals over snow may be less reliable and are, for existing missions, typically filtered or flagged for potentially poor quality.
Snow surfaces are highly forward-scattering and therefore the traditional nadir-viewing geometries over land might not be optimal and instead the strongest signal could be attainable in glint-like geometries. In addition, the contributions from the 1.6 um and 2.0 um CO2 absorption bands need to be evaluated over snow. In this work, we examine the effects of a realistic, non-Lambertian surface reflection model of snow based on snow reflectance measurements on simulated top-of-atmosphere radiances in the wavelength bands of interest. The radiance simulations were carried out with various different viewing geometries, solar angles and snow surfaces. The effect of off-glint pointing was also investigated.
There are three main findings of the simulation study. Firstly, snow reflectivity varies greatly by snow type, but the forward reflection peak is present in all examined types. Secondly, glint observation mode was found to be more reflective than nadir observation mode over snow surfaces across all the examined wavelengths bands and geometries. Thirdly, the weak CO2 band had systematically greater radiances than the strong CO2 band which could indicate a greater significance in retrievals over snow.
ESA SNOWITE is a feasibility study funded by European Space Agency for examining how to improve satellite-based remote sensing of CO2 over snow-covered surfaces. It is a cooperative project between Finnish Meteorological Institute, Finnish Geospatial Research Institute and University of Leicester. The primary aim of the project is to support the development of the planned CO2M mission.