A flexible hyperspectral simulation tool for complex littoral environments

Abstract

This work describes a visualization tool and sensor testbed that can be used for assessing the performance of both instruments and human observers in support of port and harbor security. Simulation and modeling of littoral environments must take into account the complex interplay of incident light distributions, spatially correlated boundary interfaces, bottom-type variation, and the three-dimensional structure of objects in and out of the water. A general methodology for a two-pass Monte Carlo solution called Photon Mapping has been adopted and developed in the context of littoral hydrologic optics. The resulting tool is an end-to-end technique for simulating spectral radiative transfer in natural waters. A modular design allows arbitrary distributions of optical properties, geometries, and incident radiance to be modeled effectively. This tool has been integrated as part of the Digital Imaging and Remote Sensing Image Generation (DIRSIG) model. DIRSIG has an established history in multi and hyperspectral scene simulation of terrain targets ranging from the visible to the thermal infrared (0.380 -20.0 microns). This tool extends its capabilities to the domain of hydrologic optics and can be used to simulate and develop active/passive sensors that could be deployed on either aerial or underwater platforms. Applications of this model as a visualization tool for underwater sensors or divers are also demonstrated.

Radiometric modeling of cavernous targets to assist in the determination of absolute temperature for input to process models

“…DIRSIG computes the reflected component by sampling the illumination load from the hemisphere and applying the BRDF of the material to each of these incident loading samples. The sampling is driven by the BRDF to insure important directional characteristics, such as specular lobes, are captured [6]. The emissive component is based on the gray body radiance using the surface temperature and the directional emissivity (see equation 3).…”

A comparative study of methods to solve the watchman route problem in a photon mapping-illuminated 3D virtual environment

“…Hence, a photon construction pass need not be confined to the visible light portion of the EM spectrum and may, in fact, represent any member of the EM spectrum [3].…”

“…Photon mapping is a well-established algorithm that is typically associated with graphics rendering software and is known for its ability to provide high quality, physics-accurate representations of a given virtual environment while also considering the effects of participating media [3]. Photon mapping is a two-pass algorithm comprised of constructing a photon map in the first pass and performing rendering in the second.…”

Advances in simulating radiance signatures for dynamic air/water interfaces

“…2,3 The approach taken was intended to be as flexible as possible in handling three-dimensional inhomogeneities, rather than using the plane-parallel assumptions underlying more established and efficient codes. 4 This was accomplished by using a bidirectional Monte Carlo technique referred to as "photon mapping," that connects source contributions to sensor samples (rays) via a local flux density estimate that could adapt to any in-water conditions.…”