Michelle Stephens

Optical Autocovariance Direct Detection Lidar for Simultaneous Wind, Aerosol, and Chemistry Profiling from Ground, Air, and Space Platforms

Optical Autocovariance Wind Lidar (OAWL) is a new direct-detection interferometric Doppler lidar approach that inherently enables simultaneous acquisition of multiple-wavelength High Spectral Resolution Lidar calibrated aerosol profiles (OA-HSRL). Unlike other coherent and direct detection Doppler systems, the receiver is self referencing; no specific optical frequency lock is required between the receiver and transmitter. This property facilitates frequency-agile modalities such as DIAL. Because UV laser wavelengths are accommodated, a single transmitter can simultaneously support winds, Raman, fluorescence, DIAL, and HSRL receiver channels, each sampling identical spatial and temporal volumes. LOS species flux measurements are acquired without the usual spatial and temporal sampling errors (or cost, volume, mass, power, and logistical issues) incurred by separate lidar systems, or lidars in combination with other remote or in-situ sensors. A proof of concept (POC) OAWL system has been built and demonstrated at Ball, and OAHSRL POC is in progress. A robust multi-wavelength, field-widened OAWL/OA-HSRL system is under development with planned airborne demonstration from a WB-57 in late 2010. Detailed radiometric and dynamic models have been developed to predict performance in both airborne and space borne scenarios. OA theory, development, demonstration status, advantages, limitations, space and airborne performance, and combined measurement synergies are discussed.

Multislit optimized spectrometer for ocean color remote sensing

The National Research Council’s recommended NASA Geostationary Coastal and Air Pollution Events (GEO-CAPE) science mission’s purpose is to identify “human versus natural sources of aerosols and ozone precursors, track air pollution transport, and study the dynamics of coastal ecosystems, river plumes and tidal fronts.” To achieve these goals two imaging spectrometers are planned, one optimized for atmospheric science and the other for ocean science. The NASA Earth Science Technology Office (ESTO) awarded the Multislit Optimized Spectrometer (MOS) Instrument Incubator Program (IIP) to advance a unique dispersive spectrometer concept in support of the GEO-CAPE ocean science mission. MOS is a spatial multiplexing imaging spectrometer that simultaneously generates hyperspectral data cubes from multiple ground locations enabling a smaller sensor with faster revisit times compared to traditional concepts. This paper outlines the science, motivation, requirements, goals, and status of the MOS program.

An investigation of high spectral resolution lidar measurements over the ocean

Analysis of data measured by the NASA Langley airborne High Spectral Resolution Lidar is presented focusing on measurements over the ocean. The HSRL is a dual wavelength polarized system (1064 and 532 nm) with the inclusion of a molecular backscatter channel at 532 nm. Data from aircraft flights over the Pamlico Sound out to the Atlantic Ocean, over the Caribbean west of Barbados, and off the coast of Barrow, Alaska are evaluated. Analysis of the data demonstrates that the molecular channel detects the presence of water due to its ability to differentiate the Brillouin- Mandelshtam spectrum, i.e. the scattering spectrum of water, from the Rayleigh/Mie spectrum. The characteristics of the lidar measurements over water, land, ice, and mixed ice/water surfaces are examined. Correlations of the molecular channel lidar signals with bathymetry (ocean depth) and extraction of attenuation from the HSRL lidar measurements are presented and contrasted with ocean color data.

On-orbit models of the CALIOP lidar for enabling future mission design

Validated models describing on-orbit performance of Earth sensing instruments provide understanding of the calibration of the instrument and insight that can be used to guide design choices for future missions. The success of the Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) launched as part of the CALIPSO instrument suite provides an opportunity to develop validated radiometric and integrated models of the instrument. We present validation of these models with on-orbit data and describe how these models can be used to help define instrument requirements for future active sensing missions that hope to capture both atmospheric and oceanographic properties. While designed for atmospheric returns, CALIOP data includes backscatter from land, ice, and ocean surface and from beneath the ocean surface. A radiometric model describing atmospheric returns that has been validated against CALIOP performance is extended to include ocean subsurface returns. The model output is compared with CALIOP, aircraft lidar measurements, and space-based ocean color measurements. This provides an opportunity to explore the value of space-based lidar measurements to ocean measurements and to identify the impact of laser and detector design choices on the returned lidar signal from the ocean as part of an ongoing effort to investigate oceanographic lidars.

Development of a validated end-to-end model for space-based lidar systems

LIDAR systems are becoming an important tool in many areas of remote data collection. Recently, BATC has applied their integrated modeling toolset, EOSyM (End-to-end Optical System Model), to development of a LIDAR system model. With the recent successful launch and deployment of the Calipso remote sensing instrument, an additional opportunity was present to develop a partially validated model from combined test data and measureables from the flight. The concept was to validate the CALIPSO system model and then use this tool to facilitate the system engineering process for future space-based designs. The system model includes the important physics of a laser, the CALIPSO optical prescription for the transmitter and receiver, thermoelastic disturbances, a simple atmospheric model, detection and signal processing of the data. This paper describes the model development process using EOSyM, some initial results with comparison to flight data and proposed future developments to expand its use for future missions.

Behavioral model and simulator for the Multi-slit Optimized Spectrometer (MOS)

The Multi-Slit Optimized Spectrometer (MOS) is a NASA funded Instrument Incubator Program (IIP) to advance an innovative dispersive spectrometer concept in support of the GEO-CAPE ocean science mission. As part of the instruments design and testing, we constructed a `behavioral model of the instruments optical engine which allows an end-to-end simulation from input radiances to nal product maps. Here we describe the model used for a rapid, but realistic, simulation of the MOS optical engine, and give illustrative examples of quantitatively tracking errors in the imaging chain from input radiances to bounds on nal product errors.

Multi-Slit Optimized Spectrometer: An Innovative Design for Geostationary Hyperspectral Imaging

Multi-Slit Optimized Spectrometer is a spatial multiplexing hyperspectral imager designed to reduce mission cost and risk for hyperspectral sensing from geostationary orbit. The multi-slit prism design resulting in 50% telescope aperture reduction will be presented.

Impact of near-cloud boundaries on radiometric performance of imaging sounders: an examination of FTS and dispersive spectrometer error sources

Meteorological sounding data provided by atmospheric imaging sounders have applications in weather forecasting, atmospheric chemistry, and climate monitoring. Realistic scenes for these instruments vary in both spatial and spectral content and such variations can impact the radiometric performance of these instruments. As sounders are developed to provide climate records with demanding long-term radiometric accuracy requirements, it becomes increasingly important to understand the effect of scene variations on the performance of these instruments. We have examined the noise performance and radiometric accuracy of two geostationary sounder architectures in cloudy scenes: a Fourier transform spectrometer (FTS) and a dispersive spectrometer. Factors such as stray light, ghosting, scattering, and line-ofsight jitter in the presence of scene inhomogeneities are considered. For each sounder architecture, quantitative estimates of the radiometric errors associated with sounding in cloudy scenes are made. We find that in a dispersive system the dominant error in a cloudy scene originates from ghosting within the instrument, while in an FTS the dominant error originates from scene modulation created by line-of-sight jitter in a partially cloudy scene coupling into signal modulation over the scale of the changing optical path length of the interferometer. In this paper we describe the assumptions made and the modeling performed. We also describe how each factor influences the radiometric performance for that architecture.