Operating wavelengths optimization for a spaceborne lidar measuring atmospheric CO_2

Abstract

The Advanced Space Carbon and Climate Observation of Planet Earth (A-SCOPE) mission, a candidate for the next generation of European Space Agency Earth Explorer Core Missions, aims at measuring CO(2) concentration from space with an integrated path differential absorption (IPDA) lidar. We report the optimization of the lidar instrument operating wavelengths, building on two performance models developed to assess measurement random errors from the instrument, as well as knowledge errors on geophysical and spectral parameters required for the measurement processing. A promising approach to decrease sensitivity to water vapor errors by 1 order of magnitude is reported and illustrated. The presented methods are applicable for any airborne or spaceborne IPDA lidar.

Investigations on frequency and energy references for a space-borne integrated path differential absorption lidar

“…In preparation of the A-SCOPE mission, a number of feasibility studies have been undertaken [7][8] [9]. The target and threshold mission requirements for the accuracy of the primary data product XCO 2 have been set to 0.05 ppm and 0.15 ppm, respectively, for an observation averaged over 50 km along the satellite track.…”

Atmospheric CO2 measurements with a 2-μm DIAL instrument

“…Space born differential absorption lidar (DIAL) measurements give some new opportunities to better understand the cycles of the three main greenhouse gases: CO 2 , CH 4 and water vapor. Such instruments allow monitoring these gases during day and night and at high latitude which current passive missions cannot do.…”

“…The spatially resolved data provided would better constraint the greenhouse gases transport models and help identify their sources and sink [1,2]. Then several DIAL missions are in preparation: Merlin (CNES/DLR) to measure CH 4 and ASCENDS (NASA) for CO 2 . One of the challenges of these missions is to get robust laser sources emitting at least two wavelengths (inside and outside an absorption line of the gas) to perform the DIAL measurement.…”

“…In the 2 µm spectral region, the gases of interest present particularly well-suited lines for spaceborne applications which can be efficiently addressed by solid state laser technologies [3,4]. In this paper we present long-range absorption measurements on the R30 2-µm absorption line of the CO 2 .…”

Airborne Laser Absorption Spectrometer Measurements of CO2Column Mixing Ratios: Source and Sink Detection in the Atmospheric Environment

“…We can use this to advantage by detuning the on-line frequency to a location one to three halfwidths from line center results in selective probing of the CO2 in the lower troposphere, where the CO2 mixing ratio variability of interest is the highest. (Typical weighting functions for CO2 sounding are found in references [1][2][3][4].) The JPL Laser Absorption Spectrometer (LAS) instrument probes a well characterized pressure-broadened absorption line profile at an offset of approximately two surface-pressure halfwidths in order to provide weighting functions suitable for peak response to CO2 near the surface.…”