Determining Amplitude Corrections for the Assessment of Surface Roughness Within A Lidar Footprint

The research presented in this thesis is under the context of the OSIRIS-REx mission, a NASA led asteroid sample return mission being launched in 2016 towards the asteroid 101955 Bennu. Aboard the spacecraft is the OSIRIS-REx Laser Altimeter (OLA), which is using the backscattered intensity for instrument calibration. By applying the novel solution of amplitude correction, it is possible to gain additional functionality out of this instrument. This thesis presents a simulation written by the author that accurately models laser altimeter performance. The simulation is used successfully to study OLA’s receiver to reduce error in the range measurements and to remove the effects of large-scale topographic features on the amplitude. The remaining amplitude variations will be interpreted as mineralogical or morphological variations that may impact the viability or the desirability of the site for sample collection

Using a LIDAR Vegetation Model to Predict UHF SAR Attenuation in Coniferous Forests

Attenuation of radar signals by vegetation can be a problem for target detection and GPS reception, and is an important parameter in models describing vegetation backscatter. Here we first present a model describing the 3D distribution of stem and foliage structure based on small footprint scanning LIDAR data. Secondly we present a model that uses ray-tracing methodology to record detailed interactions between simulated radar beams and vegetation components. These interactions are combined over the SAR aperture and used to predict two-way attenuation of the SAR signal. Accuracy of the model is demonstrated using UHF SAR observations of large trihedral corner reflectors in coniferous forest stands. Our study showed that the model explains between 66% and 81% of the variability in observed attenuation

Superposition of gravity waves with different propagation characteristics observed by airborne and space-borne infrared sounders

Many gravity wave analyses, based on either observations or model simulations, assume the presence of only a single dominant wave. This paper shows that there are much more complex cases with gravity waves from multiple sources crossing each others\u27 paths. A complex gravity wave structure consisting of a superposition of multiple wave packets was observed above southern Scandinavia on 28 January 2016 with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA). The tomographic measurement capability of GLORIA enabled a detailed 3-D reconstruction of the gravity wave field and the identification of multiple wave packets with different horizontal and vertical scales. The larger-scale gravity waves with horizontal wavelengths of around 400 km could be characterised using a 3-D wave-decomposition method. The smaller-scale wave components with horizontal wavelengths below 200 km were discussed by visual inspection. For the larger-scale gravity wave components, a combination of gravity-wave ray-tracing calculations and ERA5 reanalysis fields identified orography as well as a jet-exit region and a low-pressure system as possible sources. All gravity waves are found to propagate upward into the middle stratosphere, but only the orographic waves stay directly above their source. The comparison with ERA5 also shows that ray tracing provides reasonable results even for such complex cases with multiple overlapping wave packets. Despite their coarser vertical resolution compared to GLORIA measurements, co-located AIRS measurements in the middle stratosphere are in good agreement with the ray tracing and ERA5 results, proving once more the validity of simple ray-tracing models. Thus, this paper demonstrates that the high-resolution GLORIA observations in combination with simple ray-tracing calculations can provide an important source of information for enhancing our understanding of gravity wave propagation

A satellite-based radar wind sensor

The objective is to investigate the application of Doppler radar systems for global wind measurement. A model of the satellite-based radar wind sounder (RAWS) is discussed, and many critical problems in the designing process, such as the antenna scan pattern, tracking the Doppler shift caused by satellite motion, and backscattering of radar signals from different types of clouds, are discussed along with their computer simulations. In addition, algorithms for measuring mean frequency of radar echoes, such as the Fast Fourier Transform (FFT) estimator, the covariance estimator, and the estimators based on autoregressive models, are discussed. Monte Carlo computer simulations were used to compare the performance of these algorithms. Anti-alias methods are discussed for the FFT and the autoregressive methods. Several algorithms for reducing radar ambiguity were studied, such as random phase coding methods and staggered pulse repitition frequncy (PRF) methods. Computer simulations showed that these methods are not applicable to the RAWS because of the broad spectral widths of the radar echoes from clouds. A waveform modulation method using the concept of spread spectrum and correlation detection was developed to solve the radar ambiguity. Radar ambiguity functions were used to analyze the effective signal-to-noise ratios for the waveform modulation method. The results showed that, with suitable bandwidth product and modulation of the waveform, this method can achieve the desired maximum range and maximum frequency of the radar system

Single-photon counting lidar for long-range three-dimensional imaging

Single-photon time-of-flight (ToF) distance ranging lidar is a candidate technology for high-resolution depth imaging for use, for example, from airborne platforms. This approach enables low average power pulsed laser sources to be used while allowing imaging from significantly longer target ranges compared to analogue imaging. The recent availability of Geiger-mode (Gm) arrays has revolutionised photon-counting lidar as they provide single-photon full-frame data in short acquisition times. This thesis presents work on the opto-mechanical design, tolerance analysis and performance evaluation of a re-configurable single-photon counting lidar which can accommodate either a single-element single-photon avalanche photodiode (SPAD) or a 32 × 32 Gm-array. By incorporating an inter-changeable lens, the two configurations were designed to provide identical pixel resolution for both the single-pixel system and the Gm-array configurations in order to permit a performance comparison to be conducted. This is the first time that such a comparison has been reported and the lidar is one of the earliest to assess the performance of a short-wave infra-red (SWIR) Gm-array. Both detection configurations used InGaAs/InP SPAD detectors and operated at a wavelength of 1550 nm. The main benefits of operating within the SWIR band include reduced solar background, lower atmospheric loss, improved covertness, as well as improved laser eye-safety thresholds. The system estimates target range by measuring the ToF using time-correlated single-photon counting (TCSPC) and was used to produce high-resolution three-dimensional images of targets at between 800 m and 10.5 km range. The single-element system has the potential to provide improved depth resolution over the array due to a smaller timing jitter but requires longer acquisition times due to the need for two-dimensional scanning. The acquisition time of the array configuration can be up to three orders of magnitude faster than the single-element configuration but requires significantly higher average laser power levels. The Gm-array provided a simultaneous estimation of angle-of-arrival and intensity fluctuations from which a comparable strength of atmospheric turbulence could be measured. This demonstrated that Gm-arrays provide a new way of high-speed turbulence measurement with time intervals much shorter than those offered by existing scintillometers

Coherent Differential Absorption Lidar for Combined Measurement of Wind and Trace Atmospheric Gases

A lidar system was developed for making combined range-resolved measurements of wind speed and direction, water vapor concentration, and carbon dioxide concentration in the atmosphere. This lidar combines the coherent Doppler technique for wind detection and the differential absorption lidar (DIAL) technique to provide a multifunctional capability. DIAL and coherent lidars have traditionally been thought of and implemented as separate instruments, but the research reported here has shown a demonstration of combining the coherent and DIAL techniques into a single instrument using solid-state lasers. The lasers used are of Ho:Tm:YLF, which operates at a wavelength of 2 μm. This wavelength is a further advantage to the lidar, as this wavelength offers a much higher level of eyesafety than shorter wavelengths conventionally used for DIAL. Two generations are lidars are described, with the first design making combined measurement of wind and water vapor. Wind speed measurements are shown of a precision better than 1 m/s, making it useful for many meteorological applications. Water vapor concentration measurements were of 86% accuracy, requiring improvement for scientific applications. This preliminary experiment revealed the largest source of error in concentration measurement to be a lack of stability in the wavelength of the laser. This problem was solved by implementing a means to precisely control the continuous-wave laser that injection seeds a pulsed laser. The finely tunable Ho:Tm:YLF laser was stabilized to absorption lines of both carbon dioxide and water vapor using a wavelength modulation technique. Long-term stabilization to within 13.5 MHz of absorption line center is shown, representing the first frequency-stabilized laser at or within 500 run of 2μm wavelength. Results are presented on injection seeding a pulsed Ho:Tm:YLF laser to impart the tunability and stabilization to the pulsed laser output. The stabilized laser system was incorporated into a second-generation coherent DIAL to make a combined measurement of wind and carbon dioxide concentration. The DIAL measurement accuracy of concentration was improved to 29%, and designs are suggested for a further reduction in error. The absorption lines around 2-μm have recently become of great interest for a high-accuracy measurements of carbon dioxide for studies in the global carbon cycle, and the lidar demonstration and laser technology presented here are enabling first steps to meet scientific needs for carbon dioxide profiling

Publications of the Jet Propulsion Laboratory, 1988

This bibliography describes and indexes by primary author the externally distributed technical reporting, released during calendar year 1988, that resulted from scientific and engineering work performed, or managed, by the Jet Propulsion Laboratory. Three classes of publications are included: JPL publications in which the information is complete for a specific accomplishment; articles from the quarterly Telecommunications and Data Acquisition (TDA) Progress Report; and articles published in the open literature

Remote Sensing

This dual conception of remote sensing brought us to the idea of preparing two different books; in addition to the first book which displays recent advances in remote sensing applications, this book is devoted to new techniques for data processing, sensors and platforms. We do not intend this book to cover all aspects of remote sensing techniques and platforms, since it would be an impossible task for a single volume. Instead, we have collected a number of high-quality, original and representative contributions in those areas