Patricia L. Lucker

CALIPSO Lidar Description and Performance Assessment

Abstract This paper provides background material for a collection of Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP) algorithm papers that are to be published in the Journal of Atmospheric and Oceanic Technology. It provides a brief description of the design and performance of CALIOP, a three-channel elastic backscatter lidar on the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. After more than 2 yr of on-orbit operation, CALIOP performance continues to be excellent in the key areas of laser energy, signal-to-noise ratio, polarization sensitivity, and overall long-term stability, and the instrument continues to produce high-quality data products. There are, however, some areas where performance has been less than ideal. These include short-term changes in the calibration coefficients at both wavelengths as the satellite passes between dark and sunlight, some radiation-induced effects on both the detectors and the laser when passing through the South Atlant...

A vector radiative transfer model for coupled atmosphere and ocean systems based on successive order of scattering method

A vector radiative transfer model has been developed for coupled atmosphere and ocean systems based on the Successive Order of Scattering (SOS) Method. The emphasis of this study is to make the model easy-to-use and computationally efficient. This model provides the full Stokes vector at arbitrary locations which can be conveniently specified by users. The model is capable of tracking and labeling different sources of the photons that are measured, e.g. water leaving radiances and reflected sky lights. This model also has the capability to separate florescence from multi-scattered sunlight. The delta - fit technique has been adopted to reduce computational time associated with the strongly forward-peaked scattering phase matrices. The exponential - linear approximation has been used to reduce the number of discretized vertical layers while maintaining the accuracy. This model is developed to serve the remote sensing community in harvesting physical parameters from multi-platform, multi-sensor measurements that target different components of the atmosphere-oceanic system.

Inherent optical properties of the coccolithophore: Emiliania huxleyi.

A realistic nonspherical model for Emiliania huxleyi (EHUX) is built, based on electron micrographs of coccolithophore cells. The Inherent Optical Properties (IOP) of the EHUX are then calculated numerically by using the discrete dipole approximation. The coccolithophore model includes a near-spherical core with the refractive index of 1.04 + m(i)j, and a carbonate shell formed by smaller coccoliths with refractive index of 1.2 + m(i)j, where m(i) = 0 or 0.01 and j(2) = -1. The reported IOP are the Mueller scattering matrix, backscattering probability, and depolarization ratio. Our calculation shows that the Mueller matrices of coccolithophores show different angular dependence from those of coccoliths.

Lidar equation for ocean surface and subsurface

The lidar equation for ocean at optical wavelengths including subsurface signals is revisited using the recent work of the radiative transfer and ocean color community for passive measurements. The previous form of the specular and subsurface echo term are corrected from their heritage, which originated from passive remote sensing of whitecaps, and is improved for more accurate use in future lidar research. A corrected expression for specular and subsurface lidar return is presented. The previous formalism does not correctly address angular dependency of specular lidar return and overestimates the subsurface term by a factor ranging from 89% to 194% for a nadir pointing lidar. Suggestions for future improvements to the lidar equation are also presented.

Uncertainty in the bidirectional reflectance model for oceanic waters

We study the impacts of the bio-optical model variations on the angular distribution (f/Q factor) of the upwelling radiance field in ocean waters. An ocean water bio-optical model has been combined with a vector radiative transfer model to calculate the f/Q factors systematically. The f/Q factors are compared to those in [Appl. Opt.41, 6289 (2002)10.1364/AO.41.006289APOPAI1559-128X] and the differences are found to be within ±10% for 81% of the total number of cases covering all wavelengths, chlorophyll a concentrations, and solar and viewing geometries. The differences are attributed to the choice of ocean water scattering function and scattering coefficient biases. In addition, we study the uncertainty of f/Q factor due to three factors: (I) the absorption coefficient of the colored dissolved organic matter (CDOM), (II) the particle scattering coefficient, and (III) the ocean water depolarization. The impacts of ocean water depolarization on the f/Q variation is found to be negligible. If we perturb the CDOM absorption coefficient by a factor ranging from 0.1 to 10, the f/Q values vary within ±5% of the average behavior of ocean waters for 93% of the cases. If we perturb the scattering coefficients by a factor ranging from 0.5 to 2.0, the f/Q variation is within ±5% for 81% of the cases studied. This work contributes to understanding the uncertainty of ocean color remote sensing.

Exact first order scattering correction for vector radiative transfer in coupled atmosphere and ocean systems

We have developed a Vector Radiative Transfer (VRT) code for coupled atmosphere and ocean systems based on the successive order of scattering (SOS) method. In order to achieve efficiency and maintain accuracy, the scattering matrix is expanded in terms of the Wigner d functions and the delta fit or delta-M technique is used to truncate the commonly-present large forward scattering peak. To further improve the accuracy of the SOS code, we have implemented the analytical first order scattering treatment using the exact scattering matrix of the medium in the SOS code. The expansion and truncation techniques are kept for higher order scattering. The exact first order scattering correction was originally published by Nakajima and Takana.1 A new contribution of this work is to account for the exact secondary light scattering caused by the light reflected by and transmitted through the rough air-sea interface.

Cirrus direct optical depth retrieval over ocean using the a-train

We have determined the CLOUDSAT/sea spray relationship and used it to analyze cirrus clouds optical depth. Differences arise between the different sensors and need to be further investigated. The direct optical depth measurements will greatly improve our

CALIPSO space-based aerosol lidar: flight software design and planned operations paradigm

The CALIPSO (Cloud Aerosol LIDAR Infrared Pathfinder Satellite Observations) satellite is due to launch from Vandenberg AFB aboard a Delta rocket in April of 2005. CALIPSO is an international mission consisting of NASA, Ball Aerospace and the French space agency CNES. Onboard CALIPSO are three instruments, a two wavelength/two polarization lidar, an Infrared radiometer and a wide field camera. This paper will focus on the software design, development and functionality of the lidar systems including the transmitter and receiver as well as the planned operations paradigm. The operations paradigm simply stated is this: command the payload once a week with all commands being time-tagged, and receive and process health and status from the payload four (4) times per day. Science data totaling over 5 gigabytes a day is down-linked once every 24 hours. A modular approach was used in the design of the flight software where the executable code is separated into 8 loadable modules and the configuration of the individual instruments is accomplished via several loadable tables. This design scheme allows for manageable updates to the executable image and allows the science team to change and experiment with instrument configuration on an as needed basis without over stressing the command uplink system. Redundant copies of all nominal executable image files are kept onboard as is a maintenance image. The Onboard Fault Detection Isolation and Recovery (FDIR) system insures the safety of the payload and all instruments.