This paper describes an approach to utilize a multi-channel, multi-spectral electro-optic (EO) system for littoral zone
characterization. Advanced Coherent Technologies, LLC (ACT) presents their EO sensor systems for the surf zone
environmental assessment and potential surf zone target detection. Specifically, an approach is presented to determine a
Surf Zone Index (SZI) from the multi-spectral EO sensor system. SZI provides a single quantitative value of the surf
zone conditions delivering an immediate understanding of the area and an assessment as to how well an airborne optical
system might perform in a mine countermeasures (MCM) operation. Utilizing consecutive frames of SZI images, ACT
is able to measure variability over time. A surf zone nomograph, which incorporates targets, sensor, and environmental
data, including the SZI to determine the environmental impact on system performance, is reviewed in this work. ACT's
electro-optical multi-channel, multi-spectral imaging system and test results are presented and discussed.
This note presents an airborne spectral imaging system and methodology used to detect, track and monitor marine
mammal populations. The system is a four band multispectral imaging system using spectral bands tailored for maritime
imaging. This low cost, low volume, imaging sensor can be deployed on either a small unmanned air vehicle (UAV) or
any other cost efficient aircraft. Results of recent multispectral data collects over marine mammals in St. Lawrence
Seaway are presented. Species present included beluga whales as well as various species of larger baleen whales.
Narrow band polarization measurements were taken from a bridge in San Diego Harbor using the Advanced Coherent
Technologies Multi-mission Adaptable Narrowband Imaging Spectrometer (MANTIS) multichannel imaging system.
MANTIS was capable of simultaneously collecting four channels of imagery through a narrowband green (532 nm) filter
together with linear polarizers oriented at 0, 45, 90, and 135 degrees. This configuration enabled the collection of the
first three Stokes Vector elements. The data is being gathered to explore methods of calculating the sea surface Mueller
Matrix. Models, methods, and measurements are presented. Of specific interest is the deviation of the modeled data
from the measured data and its causes. The data and a model are used to estimate the contribution of upwelled polarized
PAR Government Systems Corporation (PAR) with Advanced Coherent Technologies, LLC (ACT) has developed
affordable, narrow-band polarimetry sensor hardware and software based upon the PAR Mission Adaptable Narrowband
Tunable Imaging Sensor (MANTIS). The sensor has been deployed in multiple environments. Polarimetric imagery of
the clear blue sky and the sea surface has been collected. In addition, a significant amount of calibration data has been
collected to correctly calibrate the sensor for real-time Stokes Vector imaging. Data collected with the MANTIS
polarization sensor has been compared to modeled data. The sensor hardware and software is described and some
representative collected calibration data are presented and compared to a developing model.
Surf zone measurements and airborne imagery were collected off North Carolina. The data and a surf zone index based
on the properties of water clarity, waves, and foam were used to predict imager performance for objects of varying
reflectivity and contrast.
This paper is devoted to computer simulation of random realizations of bottom images. Simulations of random images
are considered to be a straightforward way to predict bottom visibility under realistic conditions. A simplified version of
a bottom imaging model using a fast simulation algorithm has been developed. Simulated results presented here allow
the visual evaluation of image quality for different signal/noise ratio (SNR) values. We show how the simulation of
random images can be used to predict bottom visibility over a variety of environmental conditions and also determine an
optimal observation strategy.
Over the past year an index has been defined which quantifies the surf zone with respect to an electro-optical (EO) system’s ability to find targets. The purpose of this index is to both normalize the EO Mine Counter Measure (MCM) systems performance expectations to the environment in which it is tested and to assess the value of its performance in an operational environment. For example, if a given system has a Probability of Detection (PD) requirement of 90% in a clear water surf zone and is tested in murky waters the surf zone index of the murky water is used to determine what PD is required in the murky water to yield the 90% PD clear water requirement. The surf zone index is defined in this paper and expanded from the deterministic contrast transmittance as reported in earlier papers to a probabilistic approach. Examples of how to measure the index using readily available low cost spectral imagers such as PAR Government Systems Corporation’s Mission Adaptable Narrowband Tunable Imaging Spectrometer (MANTIS) system are given. Finally, the surf zone index usage is discussed and demonstrated.
Airborne multispectral imagery was collected over various targets on the beach and in the water in an attempt to characterize the surf zone environment with respect to electro-optical system capabilities and to assess the utility of very low cost, small multispectral systems in mine counter measures (MCM) and intelligence, surveillance and reconnaissance applications. The data was collected by PAR Government Systems Corporation (PGSC) at the Army Corps of Engineers Field Research Facility at Duck North Carolina and on the beaches of Camp Pendleton Marine Corps Base in Southern California. PGSC flew the first two of its MANTIS (Mission Adaptable Narrowband Tunable Imaging Sensor) systems. Both MANTIS systems were flown in an IR - red - green - blue (700, 600, 550, 480 nm) configuration from altitudes ranging from 200 to 700 meters. Data collected has been lightly analyzed and a surf zone index (SZI) defined and calculated. This index allows mine hunting system performance measurements in the surf zone to be normalized by environmental conditions. The SZI takes into account water clarity, wave energy, and foam persistence.
Collection of airborne dat can be an expensive exercise. Data flights should optimize the quality and quantity of the data collected at minimal cost. Although the site to be surveyed is fixed, a mission planner has some freedom in formulating collection strategies. Choices may include the season, the time of day, the altitude and directions of the data run flights, the spectral bands, and the spectral and spatial resolutions used for the survey. A stochastic model has been developed to simulate and quantitatively estimate the statistical performance of airborne hyper- and multi- spectral systems in imaging a littoral sea bottom through a wavy sea surface. Results include mean and variance of various measures of system performance. Candidate collection plans can be tested with the stochastic model. This paper demonstrates the use of the stochastic model in examining the effect of flight direction on the quality of imagery for a variety of zenith sun angles and surface wave conditions. The calculations show the extreme sensitivity of data quality in terms of image signal to noise ratios to flight direction, sun angle, and sea wave direction.
Multispectral and hyperspectral sensors are being used for remote sensing and imaging of ocean waters. Many applications require the compression of hyperspectral data to achieve real-time transmission or exploitation. Hyperspectral data compression or reduction has been accomplished using techniques based upon principal component analysis or linear unmixing. Alternatively, data compression (reduction) may be performed by band selection, or band selection may be preliminary to either of the other compression techniques. Band selection also has implications for sensor design and the stability of estimates of processing parameters. In this study, we address the question of which bands are the most efficacious for imaging submerged objects, such as whales, using an anomaly detector, or a matched filter. Bands are selected by optimizing a detection criterion subject to a constraint on the number of bands. The technique is applied to give hyperspectral data sets, and the optimum bandwidths and centers are determined. The loss in performance from selecting reduced numbers of bands is tabulated and the need for adaptively selecting reduced numbers of bands is demonstrated.
Airborne lidars systems have progressed to the point where they are increasingly being used in surveys and bathymetric studies of coastal and littoral zones. Scattered laser pulse light in these turbid regions hurt the performance of lidar system s as photons delayed by multiple scattering simultaneously return with the signal from a distant target. This phenomenon is called 'optical ringing' and is analogous to reverberation in acoustics. A Monte Carlo model was used to examine the effect of water turbidity on the temporal storage of photons in increasing scattering orders for an airborne lidar. The lidars modeled had combinations of both wide and narrow source and receiver fields. The lidar looked at nadir into a flat clam sea with optical properties ranging from clear to turbid water. The amount of optical ringing present in a return was proportional to the size of the pulse-illuminated in water volume. The results showed multiple scattered light surpassing single scattered light returns for all cases of source-receiver field combinations for even the clearest water studied.
A Monte Carlo model is used to examine the effect of water turbidity on the temporal storage of photons. Multiple scattering can store light in increasing scattering orders. It is hypothesized that this light will be present in a LIDAR gate when signal photons return from a distant target and will generally exceed the backscatter predicted by single scatter models. A photon's mean survival time in a turbid medium is the product of the medium's absorption coefficient at the photon's wavelength times the speed of light in the medium. For very clear ocean water this is about 190 nanoseconds. The model considers an unbounded body of water illuminated by light from a pulsed laser beam. An irradiance receiver collocated with the laser transmitter is the detector. Storage is studied as the absorption and scattering constituents of the water are incrementally varied in multiples of those found in clearest sea water. Single scatter albedos ranged from about 0.2 to 0.85 to span naturally occurring conditions. Results for this geometry show multiply scattered light surpassing singly scattered light returns for paths of the order of a volume attenuation length or less.
In this paper, we describe an experiment to measure the point spread function (PSF) of Arctic ice that was conducted by personnel of the Naval Ocean Systems Center in 1985. SRI International designed and developed the instrumentation. In April, data were collected on refrozen leads in pack ice concentrated near the Beaufort Gyre. The location was about 200 miles from the North Pole at approximately 86 degrees north and 88 degrees west. PSF measurements were made with a Hasselblad camera and a pulsed Lambertian (cosine) source gated to the camera. Recently, SRI digitized the film data with a charge-coupled device (CCD) camera and performed a digital analysis of the images. Results from two sites of new and first- year ice, 0.66 m and 2.1 m thick, respectively, are presented. Because of the strong multiple scattering by sea ice, and the limited area of the ice surface that could be imaged by the camera, the data obtained only partially characterize the PSF of the ice. The paper concludes with suggestions for improving future sea ice PSF measurements.
Measurements were made of the spread of a gaussian argon ion (489 nm) laser beam as it passed through up to 20 cm of
sea ice grown in a water tank at air temperatures of -15, -25, and -35°C. These growth temperatures were selected to cover
a range of ±10°C about the sea ice eutectic temperature of Teut = -21.2°C. The Beam Spread Function (BSF) and the
transform related Modulation Transfer Function (MTF) were obtained for increasing thicknesses of ice grown at these
temperatures. In general the BSF could be represented as the sum of a gaussian distribution of narrow width and large
amplitude due to multiple narrow angle forward scattering and a smaller wider spread associated with a growing diffuse
light field from multiple wider angle scattered light. For ice grown at all temperatures rms spread was found to follow a 3/2
power law with ice thickness. The rms spread was found to be less in the ice grown at the colder temperatures due to
increased attenuation with the smaller ice crystal size.
SC586: When Sonar Isn't Enough: Marine Optics for Port Security
This course will review the basic principles of marine optics, describe the current state of the art in marine imaging, and present future directions in optics for port and harbor security. It will also describe some of the real-world threats already encountered in port security. The marine-optics review will include effects of waves and subsurface effects on imaging underwater and seeing through the sea surface. The current state of the art section will describe active and passive sensors, including lidar, hyperspectral, and multispectral systems, with emphasis on proven technologies for mine countermeasures (MCM). The course will address some of the issues related to adapting military technology for civilian harbor and port defense.