Comparisons of aerosol backscatter using satellite and ground lidars: implications for calibrating and validating spaceborne lidar

Gimmestad, Gary G.; Forrister, H.; Grigas, Tomas; O’Dowd, Colin

doi:10.1038/srep42337

Cited by 11 publications

(9 citation statements)

References 12 publications

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“…Our rationale for this choice is described at length in V10. Recent field observations using the Raman lidar technique at both 532 and 1064 nm provide further evidence for the spectral independence of cirrus backscatter (Haarig et al, 2016), as do previous elastic backscatter lidar measurements acquired at 550 and 728 nm (Ansmann et al, 1993) and multiwavelength Raman measurements acquired at 355 and 532 nm (Beyerle et al, 2001).…”

Section: Caliop 1064 Nm Calibration Fundamentalssupporting

confidence: 65%

“…While the random uncertainties in the calibration scale factors due to χ cirrus can be reduced by averaging, χ cirrus is also a potential source of irreducible bias errors. The best available estimate of the mean value of χ cirrus remains 1.01, as determined in V10 and verified by experimentally by Haarig et al, 2016. However, the uncertainty in this estimate is large (±0.25), and the true value of χ cirrus may be somewhat different from the value used in the CALIOP V4 calibration algorithm (e.g., 1.00 vs. 1.01, which would introduce a bias of 1 % into the scale factor calculations).…”

Section: Bias Errorsmentioning

confidence: 53%

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CALIPSO lidar calibration at 1064 nm: version 4 algorithm

et al. 2019

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Abstract. Radiometric calibration of space-based elastic backscatter lidars is accomplished by comparing the measured backscatter signals to theoretically expected signals computed for some well-characterized calibration target. For any given system and wavelength, the choice of calibration target is dictated by several considerations, including signal-to-noise ratio (SNR) and target availability. This paper describes the newly implemented procedures used to calibrate the 1064 nm measurements acquired by CALIOP (i.e., the Cloud-Aerosol Lidar with Orthogonal Polarization), the two-wavelength (532 and 1064 nm) elastic backscatter lidar currently flying on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission. CALIOP's 532 nm channel is accurately calibrated by normalizing the molecular backscatter from the uppermost aerosol-free altitudes of the CALIOP measurement region to molecular model data obtained from NASA's Global Modeling and Assimilation Office. However, because CALIOP's SNR for molecular backscatter measurements is prohibitively lower at 1064 nm than at 532 nm, the direct high-altitude molecular normalization method is not a viable option at 1064 nm. Instead, CALIOP's 1064 nm channel is calibrated relative to the 532 nm channel using the backscatter from a carefully selected subset of cirrus cloud measurements. In this paper we deliver a full account of the revised 1064 nm calibration algorithms implemented for the version 4.1 (V4) release of the CALIPSO lidar data products, with particular emphases on the physical basis for the selection of “calibration quality” cirrus clouds and on the new averaging scheme required to characterize intra-orbit calibration variability. The V4 procedures introduce latitudinally varying changes in the 1064 nm calibration coefficients of 25 % or more, relative to previous data releases, and are shown to substantially improve the accuracy of the V4 1064 nm attenuated backscatter coefficients. By evaluating calibration coefficients derived using both water clouds and ocean surfaces as alternate calibration targets, and through comparisons to independent, collocated measurements made by airborne high spectral resolution lidar, we conclude that the CALIOP V4 1064 nm calibration coefficients are accurate to within 3 %.

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Section: Caliop 1064 Nm Calibration Fundamentalssupporting

confidence: 65%

Section: Bias Errorsmentioning

confidence: 53%

CALIPSO lidar calibration at 1064 nm: version 4 algorithm

et al. 2019

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“…While these studies pointed towards a possible issue with CALIOP calibration, there are significant issues involved in using ground-based lidars to validate satellite lidars, especially with regards to spatial and temporal matching. Gimmestad et al (2017) pointed out that an inherent difficulty in validating CALIOP observations is the need to average over large distances along-track to sufficiently reduce the random noise in the CALIOP measurements. A more rigorous evaluation of the CALIOP calibration was possible using airborne LaRC HSRL underflights beginning early in the CALIPSO mission, using internally calibrated data from the HSRL 532 nm channel.…”

Section: Motivation For a Revised Calibration Algorithmmentioning

confidence: 99%

“…The airborne HSRL developed at NASA LaRC (Hair et al, 2008) has been used throughout the CALIPSO mission to validate the CALIOP lidar calibration through an ongoing series of coincident underflights (Rogers et al, 2011). At 532 nm, the HSRL uses an internal calibration technique that avoids the aerosol contamination issues at calibration altitudes encountered by spaceborne lidars and thus can deliver highly accurate measurements (to within ∼ 1 %) of attenuated backscatter coefficients (Rogers et al, 2011).…”

Section: Validation Of Vcalibration: Comparisons With Hsrl Measurementsmentioning

confidence: 99%

CALIPSO lidar calibration at 532 nm: version 4 nighttime algorithm

et al. 2018

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Abstract. Data products from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) on board Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) were recently updated following the implementation of new (version 4) calibration algorithms for all of the Level 1 attenuated backscatter measurements. In this work we present the motivation for and the implementation of the version 4 nighttime 532 nm parallel channel calibration. The nighttime 532 nm calibration is the most fundamental calibration of CALIOP data, since all of CALIOP's other radiometric calibration procedures – i.e., the 532 nm daytime calibration and the 1064 nm calibrations during both nighttime and daytime – depend either directly or indirectly on the 532 nm nighttime calibration. The accuracy of the 532 nm nighttime calibration has been significantly improved by raising the molecular normalization altitude from 30–34 km to the upper possible signal acquisition range of 36–39 km to substantially reduce stratospheric aerosol contamination. Due to the greatly reduced molecular number density and consequently reduced signal-to-noise ratio (SNR) at these higher altitudes, the signal is now averaged over a larger number of samples using data from multiple adjacent granules. Additionally, an enhanced strategy for filtering the radiation-induced noise from high-energy particles was adopted. Further, the meteorological model used in the earlier versions has been replaced by the improved Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2), model. An aerosol scattering ratio of 1.01±0.01 is now explicitly used for the calibration altitude. These modifications lead to globally revised calibration coefficients which are, on average, 2–3 % lower than in previous data releases. Further, the new calibration procedure is shown to eliminate biases at high altitudes that were present in earlier versions and consequently leads to an improved representation of stratospheric aerosols. Validation results using airborne lidar measurements are also presented. Biases relative to collocated measurements acquired by the Langley Research Center (LaRC) airborne High Spectral Resolution Lidar (HSRL) are reduced from 3.6 %±2.2 % in the version 3 data set to 1.6 %±2.4 % in the version 4 release.

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“…Airborne measurements of particulate backscatter and extinction have been important for assessing CALIOP 532 nm (Powell et al, 2009;Rogers et al, 2011) and 1064 nm (Vaughan et al, 2010;2019) level 1 attenuated backscatter profiles, level 2 AOD retrievals , aerosol classification methodology (Burton et al, 2013), cirrus cloud properties (Yorks et al, 2011), and combined active (CALIOP) passive (Moderate Resolution Imaging Spectroradiometer, MODIS) retrievals of aerosol extinction profiles (Burton et al, 2010). Using airborne measurements to evaluate CALIOP aerosol backscatter measurements avoids uncertainties caused by systematic errors, spatial inhomogeneities, and distortions associated with using ground based lidar measurements for such validation (Gimmestad et al, 2017). Consequently, ACEPOL also collected measurements under the CALIOP on flights conducted on October 26 th , November 7th and 9th, and under the CATS sensor on the 19 th of October.…”

Section: Cloud-aerosol Lidar and Infrared Pathfinder Satellite Observmentioning

confidence: 99%

The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign

Knobelspiesse

Barbosa

Bradley

et al. 2020

Preprint

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Abstract. In the fall of 2017, an airborne field campaign was conducted from the NASA Armstrong Flight Research Center in Palmdale, California to advance the remote sensing of aerosols and clouds with Multi-angle Polarimeters (MAP) and Lidars. The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) campaign was jointly sponsored by NASA and the Netherlands Institute for Space Research (SRON). Six instruments were deployed on the ER-2 high altitude aircraft. Four were MAPs: the Airborne Hyper Angular Rainbow Polarimeter (AirHARP), the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI), the Airborne Spectrometer for Planetary EXploration (SPEX Airborne) and the Research Scanning Polarimeter (RSP). The remainder were Lidars, including the Cloud Physics Lidar (CPL) and the High Spectral Resolution Lidar 2 (HSRL2). The southern California base of ACEPOL enabled observation of a wide variety of scene types, including urban, desert, forest, coastal ocean and agricultural areas, with clear, cloudy, polluted and pristine atmospheric conditions. Flights were performed in coordination with satellite overpasses and ground based observations, including the Groundbased Multiangle SpectroPolarimetric Imager (GroundMSPI), sun photometers, and a surface reflectance spectrometer. ACEPOL is a resource for remote sensing communities as they prepare for the next generation of spaceborne MAP and lidar missions. Data are appropriate for algorithm development and testing, instrument intercomparison, and investigations of active and passive instrument data fusion. They are freely available to the public, at https://doi.org/10.5067/SUBORBITAL/ACEPOL2017/DATA001 (ACEPOL Science Team, 2017). This paper describes ACEPOL for potential data users, and also provides an outline of requirements for future field missions with similar objectives.

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Comparisons of aerosol backscatter using satellite and ground lidars: implications for calibrating and validating spaceborne lidar

Cited by 11 publications

References 12 publications

CALIPSO lidar calibration at 1064 nm: version 4 algorithm

CALIPSO lidar calibration at 1064 nm: version 4 algorithm

CALIPSO lidar calibration at 532 nm: version 4 nighttime algorithm

The Aerosol Characterization from Polarimeter and Lidar (ACEPOL) airborne field campaign

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