Sensitivity Study for Atmospheric Applications with Apex

The new airborne imaging spectrometer APEX will be available in 2006. It observes the visible and short-wave infrared spectral ranges. With its unique combination of spectral and spatial resolution, atmospheric molecular spectroscopy is feasible with unprecedented spatial resolution and coverage. Sensitivity calculations show, that abundances of CO2 and CH4 and pollution events of NO2 and O3 in the planetary boundary layer will be quantified with a spatial resolution of several meters. Such observations open new possibilities in the characterization of sub-satellite pixel distributions and air pollution monitoring. INTRODUCTION The APEX Instrument The Airborne Prism EXperiment (APEX) is an airborne dispersive pushbroom imaging spectrometer for the hyperspectral observation of ground reflectances [e.g. Nieke et al., 2004]. APEX is currently being built in a joint Swiss/Belgian project funded through the ESA PRODEX program. It will be operated by VITO, Belgium, starting from 2006. The spectrometer records up to 511 spectral points in the wavelength range 380–2500nm with a sampling interval of 0.4 to 10 nm. A CCD and a CMOS are used as detectors in the visible and SWIR spectral range, respectively. The ground pixel size ranges from 2 to 5m corresponding to flight altitudes of 4 to 10 km. Since APEX is a pushbroom instrument all spectral points are simultaneously observed for all 1000 across-track pixels. A dedicated calibration laboratory is being built to facilitate the absolute calibration of the instrument. For more details visit the instrument homepage http://www.apex-esa.org. Atmospheric Applications Even though APEX primarily aims at the observation of the surface reflectance, atmospheric applications have already been taken into account during the definition of the instrument requirements [Schlaepfer and Schaepman, 2002]. APEX achieves an unprecedented combination of good spatial and spectral resolutions, coverage, and signal to noise ratio. Thus a large number of atmospheric parameters may also be retrieved from its measurements. Figure 1 gives an overview of the optical depths of various atmospheric constituents in the spectral range of APEX. The values are convolved to the spectral resolution of APEX. Its center band wavelengths are indicated by vertical red lines. 1 Now at European Centre for Medium-Range Weather Forecasts, Shinfield Park, Reading, RG2 9AX, UK © EARSeL and Warsaw University, Warsaw 2005. Proceedings of 4th EARSeL Workshop on Imaging Spectroscopy. New quality in environmental studies. Zagajewski B., Sobczak M., Wrzesień M., (eds) Clouds APEX may be used to observe variations in the radiance field due to the scattering by structured clouds at spatial scales ranging from about 1m to several km simultaneously. E.g., von Savigny et al. [2002] have analyzed the radiative smoothing using a time series of zenith sky radiances under clouds. With APEX the analysis can be extended by observing a 2-dimensional field up-welling radiances over a large spectral range. Absorber Optical Depth for 316 APEX bands (VNIR)