Aperture synthesis offers the potential for high resolution images in a relatively compact system. We describe our multiaperture
IMAGE testbed which uses coherent detection to measure the complex field in spatially separated apertures.
We describe a post-detection optimization algorithm which is used to synthesize a composite image whose angular
resolution exceeds that of a single aperture. We present experimental results in which we image extended targets at a
simulated range using a compact range developed for this purpose.
Coherent high resolution imaging of distant targets is a challenging problem whose complexity involves understanding
of diffractive properties of the optical imaging system, speckle properties of target, statistical properties
of the atmospheric refractive index variations, coherence properties of the light source and noise limtations of the
detector array to mention a few major issues. In a coherent laser radar imaging system, the target is illuminated
with a laser beam, and the scattered light wave from the target light wave is mixed with a local oscillator wave
from the same source. The system is referred to as spatial heterodyne imaging system. The sparse aperture
imaging approach is based on reducing the total irradiance collection area using smaller sub-apertures, while
the resulting resolution of the sparse aperture imaging array is equivalent to an aperture larger than the subapertures.
The Ladar and Optical Communications Institute (LOCI) currently has a prototype of the high
resolution sparse aperture imaging testbed with an indoor and outdoor range capability. In collaboration with
industry partners, academic institutions, and the government this testbed is becoming an innovative research
tool in the field of high resolution coherent ladar imaging.
A modification to the mathematical representation of shadowing and obscuration (SO) in the Maxwell-Beard BRDF model is proposed to better represent actual SO data and subsequently improve the accuracy of model predicted values of BRDF. The SO function is an empirical dual peak mathematical expression originally developed for smooth first surface layer opaque material, such as semi-gloss and gloss paints. Adding variability to forward scattering of the SO function allows a better fit to more sample types. The result is a more accurate prediction of BRDF values for model non-compliant samples such as brick, concrete, asphalt, and paints with high concentrations of extender pigment. Data were collected and analyzed for both model compliant and non-compliant samples. The proposed model changes were implemented through use of an interactive spreadsheet. Results for compliant and non- compliant samples were compared using the original and modified model. Model compliant samples showed little improvement, while non-compliant samples often showed marked improvement.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.