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  • 1
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    Calibration and flight results for the Ares I-X 5-hole probe (2011)
    Elsevier
    Details
    Publication Date: 2011-04-01
    Print ISSN: 0094-5765
    Electronic ISSN: 1879-2030
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Elsevier
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    PAPER CURRENT
  • 2
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    Pseudorandom Noise Code-Based Technique for Cloud and Aerosol Discrimination Applications (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: 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 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. Keywords: ASCENDS, CO2 sensing, O2 sensing, PN codes, CW lidar
    Keywords: Optics
    Type: Paper 8037-20 , SPIE Defense, Security, and Sensing 2011 , SPIE Defense, Security, and Sensing 2011; Apr 25, 2011 - Apr 29, 2011; Orlando, FL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Pseudorandom Noise Code-Based Technique for Thin Cloud Discrimination with CO2 and O2 Absorption Measurements (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: 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 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 pseudo noise (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.
    Keywords: Lasers and Masers
    Type: NF1676L-13229
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A Low Cost Remote Sensing System Using PC and Stereo Equipment (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: 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 reasonable cost. We demonstrate its value as an instructional tool for teaching concepts of remote sensing and digital signal processing.
    Keywords: Earth Resources and Remote Sensing
    Type: NF1676L-12948
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Fourier Transform Spectrometer System (2014)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A Fourier transform spectrometer (FTS) data acquisition system includes an FTS spectrometer that receives a spectral signal and a laser signal. The system further includes a wideband detector, which is in communication with the FTS spectrometer and receives the spectral signal and laser signal from the FTS spectrometer. The wideband detector produces a composite signal comprising the laser signal and the spectral signal. The system further comprises a converter in communication with the wideband detector to receive and digitize the composite signal. The system further includes a signal processing unit that receives the composite signal from the converter. The signal processing unit further filters the laser signal and the spectral signal from the composite signal and demodulates the laser signal, to produce velocity corrected spectral data.
    Keywords: Instrumentation and Photography
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Time Shifted PN Codes for CW Lidar, Radar, and Sonar (2013)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A continuous wave Light Detection and Ranging (CW LiDAR) system utilizes two or more laser frequencies and time or range shifted pseudorandom noise (PN) codes to discriminate between the laser frequencies. The performance of these codes can be improved by subtracting out the bias before processing. The CW LiDAR system may be mounted to an artificial satellite orbiting the earth, and the relative strength of the return signal for each frequency can be utilized to determine the concentration of selected gases or other substances in the atmosphere.
    Keywords: Lasers and Masers; Earth Resources and Remote Sensing; Acoustics; Communications and Radar
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    A Comparison of Potential IM-CW Lidar Modulation Techniques for ASCENDS CO2 Column Measurements From Space (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Global atmospheric carbon dioxide (CO2) measurements through the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) Decadal Survey recommended space mission are critical for improving our understanding of CO2 sources and sinks. IM-CW (Intensity Modulated Continuous Wave) lidar techniques are investigated as a means of facilitating CO2 measurements from space to meet the ASCENDS science requirements. In previous laboratory and flight experiments we have successfully used linear swept frequency modulation to discriminate surface lidar returns from intermediate aerosol and cloud contamination. Furthermore, high accuracy and precision ranging to the surface as well as to the top of intermediate clouds, which is a requirement for the inversion of the CO2 column-mixing ratio from the instrument optical depth measurements, has been demonstrated with the linear swept frequency modulation technique. We are concurrently investigating advanced techniques to help improve the auto-correlation properties of the transmitted waveform implemented through physical hardware to make cloud rejection more robust in special restricted scenarios. Several different carrier based modulation techniques are compared including orthogonal linear swept, orthogonal non-linear swept, and Binary Phase Shift Keying (BPSK). Techniques are investigated that reduce or eliminate sidelobes. These techniques have excellent auto-correlation properties while possessing a finite bandwidth (by way of a new cyclic digital filter), which will reduce bias error in the presence of multiple scatterers. Our analyses show that the studied modulation techniques can increase the accuracy of CO2 column measurements from space. A comparison of various properties such as signal to noise ratio (SNR) and time-bandwidth product are discussed.
    Keywords: Earth Resources and Remote Sensing; Instrumentation and Photography
    Type: NF1676L-18158 , 2014 European Geosciences Union General Assembly; Apr 27, 2014 - May 02, 2014; Vienna; Austria
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    Advanced Sine Wave Modulation of Continuous Wave Laser System for Atmospheric CO2 Differential Absorption Measurements (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA Langley Research Center in collaboration with ITT Exelis have been experimenting with Continuous Wave (CW) laser absorption spectrometer (LAS) as a means of performing atmospheric CO2 column measurements from space to support the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) mission.Because range resolving Intensity Modulated (IM) CW lidar techniques presented here rely on matched filter correlations, autocorrelation properties without side lobes or other artifacts are highly desirable since the autocorrelation function is critical for the measurements of lidar return powers, laser path lengths, and CO2 column amounts. In this paper modulation techniques are investigated that improve autocorrelation properties. The modulation techniques investigated in this paper include sine waves modulated by maximum length (ML) sequences in various hardware configurations. A CW lidar system using sine waves modulated by ML pseudo random noise codes is described, which uses a time shifting approach to separate channels and make multiple, simultaneous online/offline differential absorption measurements. Unlike the pure ML sequence, this technique is useful in hardware that is band pass filtered as the IM sine wave carrier shifts the main power band. Both amplitude and Phase Shift Keying (PSK) modulated IM carriers are investigated that exibit perfect autocorrelation properties down to one cycle per code bit. In addition, a method is presented to bandwidth limit the ML sequence based on a Gaussian filter implemented in terms of Jacobi theta functions that does not seriously degrade the resolution or introduce side lobes as a means of reducing aliasing and IM carrier bandwidth.
    Keywords: Lasers and Masers
    Type: NF1676L-17341 , Applied Optics; 53; 5; 816-829
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Calibration and Flight Results for the Ares I-X 5-Hole Probe (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: Flight and calibration results are presented for the Ares I-X 5-hole probe. The probe is calibrated by using a combination of wind tunnel, CFD, and other numerical modeling techniques. This is then applied to the probe flight data and comparisons are made between the vanes and 5-hole probe. Using this and other data it is shown the probe was corrupted by water rendering that measurement unreliable.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: NF1676L-10448
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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