Michael A. Flood

Pseudorandom Noise Code-Based Technique for Thin Cloud Discrimination with CO2 and O2 Absorption Measurements

NASA Langley Research Center is working on a continuous wave (cw) laser-based remote sensing scheme for the detection of CO2 and O2 from space-based platforms suitable for an active sensing of CO2 emissions over nights, days, and seasons (ASCENDS) mission. ASCENDS is a future space-based mission to determine the global distribution of sources and sinks of atmospheric carbon dioxide (CO2). A unique, multifrequency, intensity modulated cw laser absorption spectrometer operating at 1.57 μm for CO2 sensing has been developed. Effective aerosol and cloud discrimination techniques are being investigated in order to determine concentration values with accuracies less than 0.3%. In this paper, we discuss the demonstration of a pseudonoise code-based technique for cloud and aerosol discrimination applications. The possibility of using maximum length sequences for range and absorption measurements is investigated. A simple model for accomplishing this objective is formulated. Proof-of-concept experiments carried out using a sonar-based LIDAR simulator that was built using simple audio hardware provided promising results for extension into optical wavelengths.

A low cost remote sensing system using PC and stereo equipment

A system using a personal computer, speaker, and a microphone is used to detect objects, and make crude measurements using a carrier modulated by a pseudorandom noise (PN) code. This system can be constructed using a personal computer and audio equipment commonly found in the laboratory or at home, or more sophisticated equipment that can be purchased at a reasonable cost. We demonstrate its value as an instructional tool for teaching concepts of remote sensing and digital signal processing.

An update on the NAST-I airborne FTS

The NPOESS / NASA Airborne Sounder Testbed - Interferometer (NAST-I) is a well-proven airborne remote sensing system, which has flown in 18 previous field campaigns aboard the high altitude NASA ER-2, Northrop Grumman / Scaled Composites Proteus, and NASA WB-57 aircraft since initially being flight qualified in 1998. While originally developed to provide experimental observations needed to finalize specifications and test proposed designs and data processing algorithms for the Cross-track Infrared Sounder (CrIS) to fly on the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project (NPP) and the Joint Polar Satellite System, JPSS (formerly NPOESS, prior to recent program restructuring), its unprecedented data quality and system characteristics have contributed to a variety of atmospheric research and measurement validation objectives. This paper will provide a program overview and update, including a summary of measurement system capabilities, select scientific results, and recent refurbishment activities.

Pseudorandom noise code-based technique for cloud and aerosol discrimination applications

NASA Langley Research Center is working on a continuous wave (CW) laser based remote sensing scheme for the detection of CO2and O2 from space based platforms suitable for ACTIVE SENSING OF CO2 EMISSIONS OVER NIGHTS, DAYS, AND SEASONS (ASCENDS) mission. ASCENDS is a future space-based mission to determine the global distribution of sources and sinks of atmospheric carbon dioxide (CO2). A unique, multi-frequency, intensity modulated CW (IMCW) laser absorption spectrometer (LAS) operating at 1.57 micron for CO2 sensing has been developed. Effective aerosol and cloud discrimination techniques are being investigated in order to determine concentration values with accuracies less than 0.3%. In this paper, we discuss the demonstration of a PN code based technique for cloud and aerosol discrimination applications. The possibility of using maximum length (ML)-sequences for range and absorption measurements is investigated. A simple model for accomplishing this objective is formulated, Proof-of-concept experiments carried out using SONAR based LIDAR simulator that was built using simple audio hardware provided promising results for extension into optical wavelengths.

Overview of laboratory testing results for an imaging Fabry-Perot interferometer

An airborne imaging Fabry-Perot Interferometer (FPI) system was developed within NASAs Instrument Incubator Program (IIP) to mitigate risk associated with implementation of such a device in future space-based atmospheric remote sensing missions. This system is focused on observing tropospheric ozone through measuring a narrow spectral interval within the strong 9.6 micron infrared ozone band at high spectral resolution, while the concept and technology also have applicability toward measurement of other trace species and other applications. The latest results from laboratory testing and characterization of enabling subsystems and the overall instrument system will be reported, with an emphasis placed on testing performed to evaluate system-level radiometric, spatial, and spectral measurement fidelity.

Performance improvement and characterization activities for an imaging Fabry-Perot interferometer

Risk mitigation activities for a prototype imaging Fabry-Perot Interferometer (FPI) system, development originating within NASAs Instrument Incubator Program (IIP) for enabling future space-based atmospheric composition missions, are continuing at NASA Langley Research Center. The system concept and technology are focused on observing tropospheric ozone around 9.6 micron, but also have applicability toward measurement of other trace species in different spectral regions and other applications. The latest results from performance improvement and laboratory characterization activities will be reported, with an emphasis placed on testing performed to evaluate system-level radiometric, spatial, and spectral measurement fidelity.

Advancement of optical component control for an imaging Fabry-Perot interferometer

Risk mitigation activities associated with a prototype imaging Fabry-Perot Interferometer (FPI) system are continuing at the NASA Langley Research Center. The system concept and technology center about enabling and improving future space-based atmospheric composition missions, with a current focus on observing tropospheric ozone around 9.6 micron, while having applicability toward measurement in different spectral regions and other applications. Recent activities have focused on improving an optical element control subsystem to enable precise and accurate positioning and control of etalon plates; this is needed to provide high system spectral fidelity critical for enabling the required ability to spectrally-resolve atmospheric line structure. The latest results pertaining to methodology enhancements, system implementation, and laboratory characterization testing are discussed.

Testing and characterization of a multispectral imaging Fabry-Perot interferometer for tropospheric trace species detection

The Tropospheric Trace Species Sensing Fabry-Perot Interferometer (TTSS-FPI) was a NASA Instrument Incubator Program (IIP) project for risk mitigation of enabling concepts and technology applicable to future NASA Science Mission Directorate atmospheric chemistry measurements. Within IIP an airborne sensor was developed and laboratory-tested to demonstrate the instrument concept and enabling technologies that are also applicable to the desired geostationary-based implementation. The concept is centered about an imaging Fabry-Perot interferometer (FPI) observing a narrow spectral interval within the strong 9.6 micron ozone infrared band with a spectral resolution ~0.07 cm-1, and also has applicability to and could simplify designs associated with sensors targeting measurement of other trace species. Results of testing and characterization of enabling subsystems and the overall instrument system are reported; emphasis is placed on recent laboratory testing performed to evaluate system-level radiometric, spatial, and spectral measurement fidelity.

Spaceflight instrument study for tropospheric ozone measurement

Space-based detection and monitoring of tropospheric ozone is critical for enhancing scientific understanding of creation and transport of this important trace gas and for providing data needed to help develop national and international strategies for mitigating impact of exposure to elevated concentrations of tropospheric ozone in the US and elsewhere. Spaceflight instrument concept studies presented here show that a spaceborne imaging Fabry-Perot interferometer to measure tropospheric ozone from geosynchronous earth orbit is feasible and can be ready for full scale development starting in 2007.

Trace Tropospheric Species Sensing-Fabry-Perot Interferometer (TTSS-FPI): spaceborne sensor concept studies for measuring tropospheric ozone

We present results of studies of instrument concepts for a spaceborne imaging Fabry-Perot interferometer to measure tropospheric ozone. Ozone is recognized as one of the most important trace constituents of the troposphere. Tropospheric ozone is responsible for acute and chronic human health problems and contributes toward destruction of plant and animal populations. Furthermore, it is a greenhouse gas and contributes toward radiative forcing and climate change. Tropospheric ozone levels have been increasing and will continue to do so as concentrations of precursor gases (oxides of nitrogen, methane, and other hydrocarbons) necessary for the photochemical formation of tropospheric ozone continue to rise. Space-based detection and monitoring of tropospheric ozone is critical for enhancing scientific understanding of creation and transport of this important trace gas and for providing data needed to help develop strategies for mitigating impacts of exposure to elevated concentrations of tropospheric ozone. Measurement concept details are discussed in a companion paper by Larar et al. Development of an airborne prototype instrument for this application is discussed by Cook et al. in another companion paper.