SUMMARY The NASA ASCENDS mission (Active Sensing of CO2 Emissions over Nights, Days, and Seasons) seeks to map global CO2 tropospheric mixing ratios from a Low-Earth Orbiting (LEO) platform using new laserbased remote sensors that directly measure integrated path differential absorption (IPDA) on and off a suitable CO2 absorption line, and then convert this optical depth measurement to spatial concentration knowledge, using ancillary temperature, water vapor and surface pressure data to determine weighted column mixing ratios. As such, the mission requires very accurate column content measurement of atmospheric CO2 concentration (<2 ppmV precision over the total column) from an active sensor in low earth orbit. Several candidate sensor solutions are currently being evaluated via concurrent airborne tests, involving sensors with continuous wave (CW) and pulsed waveforms at both 1.5 and 2 micron wavelengths. While both wavelength choices have their benefits and disadvantages, there is a growing trend to favor the two micron solution in order to have a column content measurement that is strongly biased to the planetary boundary layer (PBL) where concentration variation due to the presence of underlying sources and sinks is most measurable. There is also a growing requirement for range-resolved capability to differentiate the primary signal return (from the ground surface) from undesired return from sub-visual Cirrus cloud that biases the column content concentration measurement.
© 2012 Optical Society of AmericaPDF Article
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