Airborne measurements of CO<sub>2</sub> column concentrations made with a pulsed IPDA lidar using a multiple-wavelength-locked laser and HgCdTe APD detector

Abstract

Abstract. Here we report on measurements made with an improved CO 2 Sounder lidar during the ASCENDS 2014 and 2016 airborne campaigns. The changes made to the 2011 version of the lidar included incorporating a rapidly wavelength-tunable, step-locked seed laser in the transmitter, using a much more sensitive HgCdTe APD detector and using an analog digitizer with faster readout time in the receiver. We also improved the lidar's calibration approach and the XCO 2 retrieval algorithm. The 2014 and 2016 flights were made over several types of topographic surfaces from 3 to 12 km aircraft altitudes in the continental US. The results are compared to the XCO 2 values computed from an airborne in situ sensor during spiral-down maneuvers. The 2014 results show significantly better performance and include measurement of horizontal gradients in XCO 2 made over the Midwestern US that agree with chemistry transport models. The results from the 2016 airborne lidar retrievals show precisions of ∼ 0.7 parts per million (ppm) with 1 s averaging over desert surfaces, which is an improvement of about 8 times compared to similar measurements made in 2011. Measurements in 2016 were also made over fresh snow surfaces that have lower surface reflectance at the laser wavelengths. The results from both campaigns showed that the mean values of XCO 2 retrieved from the lidar consistently agreed with those based on the in situ sensor to within 1 ppm. The improved precision and accuracy demonstrated in the 2014 and 2016 flights should benefit future airborne science campaigns and advance the technique's readiness for a spacebased instrument.

A singular value decomposition framework for retrievals with vertical distribution information from greenhouse gas column absorption spectroscopy measurements

“…Note that use of a uniform column for vertical information is equivalent to the use of an uninformative prior. used the prior distribution for regularizing the CO 2 retrievals but the SVD-reduced dimensionality for CH 4 Melroy et al 2015Fixed profile measurement uniform Others spectrometers (CO 2 , CH 4 ) Yuan et al 2015Fixed profile measurement prior Si-Yang et al 2013Petri et al 2012Airborne IPDA lidars CO 2 MFLL Lin et al (2015) Fixed profile measurement prior (< 10 −3 cm −1 ) CO 2 LAS Menzies et al (2014) Fixed profile measurement prior CO 2 Sounder Abshire et al (2018) Fixed profile measurement uniform CH 4 Sounder Riris et al (2012) Fixed profile measurement uniform 2 µm CO 2 IPDA Refaat et al (2016) Fixed profile measurement prior CHARM-F…”

“…GHG column remote-sensing measurements are made using satellitebased optical spectrometers such as those aboard the Greenhouse gas Observing Satellite (GOSAT, Kuze et al, 2009) and the Orbiting Carbon Observatory (OCO-2, Boesch et al, 2011), ground-based spectrometers such as the Total Column Carbon Observing Network (TCCON, Wunch et al, 2011) and other instruments (Gisi et al, 2012). Atmospheric measurements have also been made using airborne integrated path differential absorption (IPDA) lidar instruments (Abshire et al, 2018;Lin et al, 2015;Menzies et al, 2014;Refaat et al, 2016). While column-averaged mixing ratios are retrieved from measurements using methods ranging from simple differential absorption ratioing (Refaat et al, 2016), least-squares line-fitting (Wunch et al, 2011) and traditional optimal estimation (OE) (Connor et al, 2008), information about the GHG vertical distribution (which we shall refer to as vertical information) is more difficult to obtain and typically not routinely reported as part of GHG retrievals.…”

HgCdTe avalanche photodiode array detectors with single photon sensitivity and integrated detector cooler assemblies for space lidar applications

“…As part of this work, DRS produced a batch of 4 × 4 pixel HgCdTe APD arrays that demonstrated nearly quantum-limited detector performance. 2 These detectors were successfully used in NASA GSFC's airborne CO 2 lidar at 1.57 μm, 3 its airborne CH 4 lidar at 1.65 μm, 4 and in the NASA Langley Research Center airborne CO 2 lidar at 2.05 μm. 5 DRS also produced a set of 2 × 8 pixel prototype APD arrays with lower dark current and higher APD gains, which enabled LMPC.…”

“…Detector active area surface map obtained via a raster scan of the laser spot while measuring the photon counts of the of FPA-A8327-14-1, pixel(1,3). The APD bias voltage is set to 11.5 V.…”

Optical Energy Variability Induced by Speckle: The Cases of MERLIN and CHARM-F IPDA Lidar

“…In the last decade, many studies have been done on the use of doubled-pulsed IPDA lidar to measure CO2 or CH4 atmospheric content from space [8][9][10] and many IPDA ground based and airborne demonstrators are been developed around the word by DLR [11][12], NASA Langley [13][14][15][16][17][18][19][20] and JPL [21][22], NIST [23][24], Tokyo Metropolitan University [25][26] or Chinese Academy of Sciences [27].…”