Now showing items 1-10 of 10

• #### Cloud Detection And Trace Gas Retrieval From The Next Generation Satellite Remote Sensing Instruments

The objective of this thesis is to develop a cloud detection algorithm suitable for the National Polar Orbiting Environmental Satellite System (NPOESS) Visible Infrared Imaging Radiometer Suite (VIIRS) and methods for atmospheric trace gas retrieval for future satellite remote sensing instruments. The development of this VIIRS cloud mask required a flowdown process of different sensor models in which a variety of sensor effects were simulated and evaluated. This included cloud simulations and cloud test development to investigate possible sensor effects, and a comprehensive flowdown analysis of the algorithm was conducted. In addition, a technique for total column water vapor retrieval using shadows was developed with the goal of enhancing water vapor retrievals under hazy atmospheric conditions. This is a new technique that relies on radiance differences between clear and shadowed surfaces, combined with ratios between water vapor absorbing and window regions. A novel method for retrieving methane amounts over water bodies, including lakes, rivers, and oceans, under conditions of sun glint has also been developed. The theoretical basis for the water vapor as well as the methane retrieval techniques is derived and simulated using a radiative transfer model.
• #### Crustal Deformation Along The San Andreas Fault And Within The Tibetan Plateau Measured Using Gps

Using the Global Positioning System (GPS), we study crustal deformation along the San Andreas Fault (SAF) in the San Francisco Bay area and within the Tibetan Plateau, and provide new constraints for the kinematics of these actively deforming plate boundaries. GPS measurements in 1996 and 1997 and Electronic Distance Measuring (EDM) data from the 1970s and 1980s at sites along the SAF in northern California were used to determine the near-fault strain rate and to investigate the slip rate, locking depth, and rheology. We found a pronounced high near-fault shear strain rate that can be explained by a 2-D inhomogeneous model in which a low-rigidity compliant zone concentrates strain near the fault. We suggest that the materials on either side of the fault and the cumulative fault offset play a role in the development of the compliant zone. If such a compliant zone is present but unmodeled, the geodetic estimates of slip rate and locking depth (seismogenic depth) would be biased. This would lead to a miscalculated seismic hazard. Thirteen GPS sites in southern Tibet, surveyed in 1995, 1998 and 2000, were merged with other data from China and Nepal into a single, self-consistent velocity field. The Himalaya and southern Tibet was modeled using a kinematically-consistent block model and elastic dislocation theory. We show a significantly lower convergence rate between India and Eurasia in central Himalaya than that previously estimated. We observe that southern Tibet undergoes non-uniform (spatial) east-west extension with one-half of the extension across the Yadong-Gulu rift. We infer that spatially non-uniform extension in southern Tibet results in variation of the arc-normal convergence rates along the Himalaya, and that the Yarlung-Zangbo suture or adjacent structure may be active as a right-lateral strike slip fault. From 44 GPS sites in the Tibetan Plateau, we show that deformation of Tibet is distributed and strain accumulation is spatially uniform across the entire plateau. We propose a kinematic model for the Tibetan Plateau to be a combination of rigid block motion, pure shear and uniaxial contraction in the direction of about N32�E, comparable to the convergence direction between India and Eurasia.
• #### Deformation Of Alaskan Volcanoes Measured Using Sar Interferometry And Gps

Geodetic measurements using the Global Positioning System (GPS) and synthetic aperture radar interferometry (InSAR) show deformation of Okmok, Westdahl, and Fisher volcanoes in the Alaska-Aleutian arc. This thesis shows the variety of deformation signals observed, presents models for the observations, and interprets them in terms of underlying processes. InSAR data show deflation of Okmok caldera during its last eruption in 1997, preceded and followed by inflation of smaller magnitude. Modeling shows that the main deformation source, interpreted as a central magma reservoir, is located at 2.5 to 5.0 km depth beneath the approximate center of the caldera, and 5 km away from the active vent. Mass balance calculations and comparison with the long-term eruptive frequency indicate that Okmok may be supplied with magma continuously from a deep source. GPS measurements between 1998 and 2001 show inflation of Westdahl volcano, with a source located about 7 km beneath the summit. The combined subsurface volume increase measured during the GPS and an earlier InSAR observation period [Lu et al., 2000a] accounts for at least 15% more than the volume erupted from Westdahl in 1991--92, suggesting that an eruption of that size could occur at any time. Neighboring Fisher caldera shows subsidence and contraction across the caldera center that is not related to any eruptive activity. The main mechanisms to explain this deformation are degassing and contractional cooling of a shallow magma body, or depressurization of Fisher's hydrothermal system, possibly triggered by an earthquake in the vicinity of the caldera in 1999. A systematic coherence analysis of SAR interferograms documents the cooling history of the 1997 Okmok lava flow. The flow is incoherent directly after emplacement, but coherence increases as more time has passed since the eruption, and also the shorter the period spanned by the interferogram. Coherence is regained three years after the eruption. This corresponds to the time when the 20 m thick flow has solidified, indicating that flow mobility is the dominant factor degrading coherence on young lava flows. Based on these results, InSAR coherence analysis can be used to derive the minimum thickness of a lava flow.
• #### Ecological and physiological aspects of caribou activity and responses to aircraft overflights

I investigated the use of remote-sensing of caribou (Rangifer tarandus) activity to assess disturbance of low-altitude overflights by jet aircraft. Resource management agencies are concerned about the potential effects of these overflights on important species of ungulates. I hypothesized that low-altitude overflights would affect activity and movements of caribou, and thereby constitute a disturbance with negative consequences on energetics. I used caribou of the Delta Herd (DCH) and captive animals at the Large Animal Research Station (LARS) to address the hypotheses: caribou (1) exhibit equal activity day and night; (2) do not time activity to light; and (3) activity patterns do not change seasonally in response to daylength. Caribou were nychthemeral and exhibited uniform activity with no apparent timing to light. DCH caribou responded to seasonal changes in the environment by modifying activity (increased activity in response to insect harassment), whereas LARS caribou altered activity in response to fluctuating physiological variables (increased activity during rut). Changes in daylength did not affect activity. Data on activity from LARS and DCH caribou were compared with extant data on caribou of the Denali and Porcupine herds. Poor quality forage in winter was inferred from long resting bouts, and low availability of forage was inferred from long active bouts of post-calving caribou of the DCH. In midsummer, caribou of the DCH exhibited significantly longer active and shorter resting bouts than did LARS caribou, consistent with a moderate level of insect harassment. Responses of caribou to overflights were mild in late winter and, thus, overflights did not constitute a disturbance. Post-calving caribou responded to overflights by increasing daily activity, linear movements, incremental energy cost, and average daily metabolic rate. Energetic responses and movements were significantly related to the loudest overflight of the day. In the insect season, activity levels increased significantly in response to overflights but with no corresponding increase in linear movements or energetics. My recommendations are to prohibit aircraft overflights of caribou during calving and post-calving periods and during key feeding times in insect harassment seasons. Research indicates the possibility of more severe effects in nutritionally stressed animals.
• #### Extent, timing, and paleogeographic significance of multiple Pleistocene glaciations in the Bering Strait region

The Dynamics Explorer mission returned a wealth of information from its two orbiting platforms. Of interest here are the three scanning photometers aboard the high-altitude platform DE-1, which obtained hundreds of thousands of global images of Earth, beginning in September of 1981, while using broad- and narrow-band filters to isolate particular terrestrial emissions. The far-ultraviolet (FUV) emissions include the line emissions of OI (130.4 and 135.6 nm) and the band emissions of $\rm N\sb2$ LBH, the brightness of each yielding information on the composition of the upper atmosphere. The OI emissions are related to the column density of atomic oxygen in the upper-atmosphere as well as the abundance of thermospheric $\rm N\sb2,$ both of which are affected by geomagnetic processes. This thesis presents a model of the DE-1 response to the OI emissions during periods of low geomagnetic activity and uses this model for studies of thermospheric response to geomagnetic storms and substorms. Variations in brightness observed after geomagnetic events are most often seen as decreases corresponding to reduced thermospheric O column densities. The relation between compositional variations in the morning sector at middle latitudes and the orientation of the magnetic field embedded in the solar wind is investigated. The orientation, which strongly affects the circulation of the thermosphere at high latitudes where these variations originate, is shown to be a significant parameter. Variations in brightness within the southern polar cap are investigated in the first study of its kind, demonstrating 20-30% decreases in brightness with the onset of magnetic activity and revealing structure in composition over distances on the order of ${\sim}300$ km. Compositional disturbances are observed immediately after heating takes place, demonstrating for the first time that an FUV instrument can detect changes in thermospheric composition on time scales under one hour. During these events, mid-latitude composition often remains relatively unperturbed. The first survey of FUV images to include ground-based measurements of ionospheric properties demonstrates that decreases in OI brightness correspond to decreases in peak F2 electron densities, known to be related to the ratio of the densities of O and $\rm N\sb2.$