Polarimetric imaging sensors in the electro-optical region, already military and commercially available in both the visual and infrared, show enhanced capabilities for advanced target detection and ...

Optical polarization - Background and Camouflage

Important properties for camouflage materials can be summarized in six criteria: (1) spectrally selective reflectance, (2) low gloss, (3) low degree of polarization, (4) low infrared emissivity, (5) non-destructive effect on radar properties and (6) color adaptivity. We have studied a collection of natural materials for potential use as camouflage surfaces for the arctic region. The four first camouflage criteria are analyzed using spectrometry, scatterometry and spectroscopic ellipsometry techniques. The materials involved in the study are diffuse white nature-inspired surfaces: Cuticles of the beetle Cyphochilus insulanus, and foams of freeze-casted cellulose nanofibrils. We present data that partly fulfills the addressed camouflage criteria. An adequate reflectance is achieved in the spectral range of 400–1600 nm for both samples. Scattering data show that near-Lambertian properties are achieved at 633 nm for both surfaces but at 1550 nm for only the beetle cuticle. The degree of polarization is low for unpolarized light incident near the surface normal for both surfaces.

Optical studies of white organic materials for camouflage applications in Arctic environments

Scene simulations of optical signature properties using signature codes normally requires input of various parameterized
measurement data of surfaces and coatings in order to achieve realistic scene object features. Some of the most important
parameters are used in the model of the Bidirectional Reflectance Distribution Function (BRDF) and are normally
determined by surface reflectance and scattering measurements. Reflectance measurements of the spectral Directional
Hemispherical Reflectance (DHR) at various incident angles can normally be performed in most spectroscopy labs,
while measuring the BRDF is more complicated or may not be available at all in many optical labs. We will present a
method in order to achieve the necessary BRDF data directly from DHR measurements for modeling software using the
Sandford-Robertson BRDF model. The accuracy of the method is tested by modeling a test surface by comparing results
from using estimated and measured BRDF data as input to the model. These results show that using this method gives no
significant loss in modeling accuracy.

Jan Fagerström

Papers

Simplifying BRDF input data for optical signature modeling