During fall periods in 2002, 2003 and 2004 three major oceanographic expeditions were carried out
in Mamala Bay, Hawaii. These were part of the RASP Remote Anthropogenic Sensing Program.
Ikonos and Quickbird optical satellite images of sea surface glint revealed ≈100 m spectral
anomalies in km2 averaging patches in regions leading from the Honolulu Sand Island Municipal
Outfall diffuser to distances up to 20 km. To determine the mechanisms behind this phenomenon,
the RASP expeditions monitored the waters adjacent to the outfall with an array of hydrographic,
optical and turbulence microstructure sensors in anomaly and ambient background regions. Drogue
tracks and mean turbulence parameters for 2 × 104 microstructure patches were analyzed to
understand complex turbulence, fossil turbulence and zombie turbulence near-vertical internal wave
transport processes. The dominant mechanism appears to be generic to stratified natural fluids
including planet and star atmospheres and is termed beamed zombie turbulence maser action
(BZTMA). Most of the bottom turbulent kinetic energy is converted to ≈ 100 m fossil turbulence
waves. These activate secondary (zombie) turbulence in outfall fossil turbulence patches that
transmit heat, mass, chemical species, momentum and information vertically to the sea surface for
detection in an efficient maser action. The transport is beamed in intermittent mixing chimneys.
The real-time simulation of broken and distorted images of a submerged target observed through a random realization of wind roughened sea surface produced by airborne gating imaging lidar is presented. The user is allowed to watch the sequence of images at the computer screen, which the lidar operator vies sat the TC screens of an operating airborne imaging lidar. Th inclusion of all types of noise as well as spatial correlation of receiver noise and noise due to a windy roughened sea surface with detailed treatment of seawater scattering provides a very realistic model. Two image processing techniques to deal with actual images - Matched Filter and Optimal Integration - are compared as to signal-to-noise ratio and probability of detection. Optimal Integration is appropriate for use by an experienced lidar operator.
KEYWORDS: LIDAR, Signal to noise ratio, Imaging systems, Receivers, Scattering, Light scattering, Data modeling, Pulsed laser operation, Sensors, Wind energy
Our previous comparisons of the SNR and resolving power of various lidar approaches used modulation transfer functions to estimate the effects of surface waves. That technique yields statistical performance estimates, but gives little insight into the appearance of individual images. This paper presents a complementary method, simulating images for the various systems. The images are generated with a numerical code combining ray tracing and small-angle scattering theory with a state-of-the-art, dynamic, surface-wave generator. The resulting images realistically simulate the refractive effects of the ocean waves, providing visual confirmations of our previous analytical results. They demonstrate the excellent contrast of a STIL for high-resolution image classification. However, the superior energy utilization of the LRG approach, makes it a better method for airborne lidar imaging, with an advantage that grows exponentially with depth. Likewise, a compact rectangular array of time- resolved pixels perform search tasks better than does a STIL. These simulations will also allow us to develop optimal strategies for image-by-image processing of LIDAR data.
On the base of a newly developed theory of image formation, which includes the effect of shadowing of the space behind an illuminated and observed object, the receiver time gating of an airborne ocean lidar system is simulated. Depending on the timing of the start of the gate, a reflected target or its shadow may be seen. The contrast and signal-to-noise ratio (SNR), for an image of the directly observed object (reflection) and the image of its shadow (obscuration), are compared. It is shown that in many cases the SNR of the object in the `shadow' (obscuration) mode can be greater than the SNR of the object observed in reflection compared at the same depth. In addition, the obscuration mode is advantageous for improving system performance in cases involving a priori choices of the start and duration of the gate. These advantages are most pronounced while observing an object in turbid shallow water through a windy roughened sea surface.
In recent years, broad area imaging lidar systems have been applied for ocean applications. These lidar have now been operated in the field since 1988. These systems possess certain intrinsic advantages over narrow angle systems, and can measure, while deployed, the very oceanographic properties on which their performance depends.
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