Preprints
https://doi.org/10.5194/egusphere-2025-3141
https://doi.org/10.5194/egusphere-2025-3141
25 Jul 2025
 | 25 Jul 2025
Status: this preprint is open for discussion and under review for Atmospheric Measurement Techniques (AMT).

CALIPSO 1064 nm Calibration Biases Inferred from Wavelength-Dependent Signal Attenuation by Stratospheric Aerosols

Jayanta Kar, Mark A. Vaughan, Robert P. Damadeo, Mahesh Kovilakam, Jason L. Tackett, and Charles R. Trepte

Abstract. Calibration of lidar signals at 1064 nm from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite depends on the prior calibration of the primary 532 nm channel. However, the 1064 nm calibration procedure also requires knowledge of the ratio of stratospheric signal attenuations at 1064 nm and 532 nm, which is not available a priori and thus is assumed to be 1. This assumption introduces a potential bias in the computed 1064 nm calibration coefficients. In this work we assess this bias by using independent multi-channel occultation retrievals of stratospheric aerosol extinction from the Stratospheric Aerosol and Gas Experiment (SAGE III) on the International Space Station (ISS) for the period 2017 onwards. We also use the GLObal Space based Stratospheric Aerosol Climatology (GloSSAC) to provide a historical background during the SAGE II era (1984 through 2005). The results show that the magnitude of the CALIOP 1064 nm calibration bias is less than 1–2 % within the tropics under stratospheric background conditions. However, recent biases can be as high as 5 % when volcanic perturbations and/or pyro-cumulonimbus (pyroCb) injections dominate the stratospheric aerosol loading. We explore the effects of this bias on CALIOP’s level 2 science retrievals by estimating the anticipated perturbations in cloud-aerosol discrimination (CAD) performance and by quantifying the non-linear propagation of errors in CALIOP’s 1064 nm extinction coefficients. This global characterization of the spectral attenuation differences should provide useful information for future spaceborne elastic lidars operating at 1064 nm.

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Jayanta Kar, Mark A. Vaughan, Robert P. Damadeo, Mahesh Kovilakam, Jason L. Tackett, and Charles R. Trepte

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Jayanta Kar, Mark A. Vaughan, Robert P. Damadeo, Mahesh Kovilakam, Jason L. Tackett, and Charles R. Trepte
Jayanta Kar, Mark A. Vaughan, Robert P. Damadeo, Mahesh Kovilakam, Jason L. Tackett, and Charles R. Trepte

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Short summary
This paper assesses a possible bias in calibration of the spaceborne CALIOP lidar signals at 1064 nm resulting from relative attenuation of the signals at 1064 nm and 532 nm due to stratospheric aerosols. Multi-channel aerosol measurements from SAGE III instrument on ISS indicate that the bias is less than 1–2 % for background conditions and up to 5 % for strong stratospheric loading. Implications for extinction retrievals at 1064 nm and cascading errors for multi-layer scenes are discussed.
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