Canopy cover is a significant factor in assessing the performance of target detection algorithms in forested environments.
This is true of electro-optical (EO), radar frequency (RF), light detection and ranging (LIDAR), multi/hyperspectral
(MSI/HSI), and other remote sensing methods. This research compares traditional ground based methods of estimating
canopy closure with estimates of canopy cover via spectral detection methods applied to VNIR/SWIR hyperspectral
imagery. This paper uses canopy cover and canopy closure as defined by Jennings, et al. . In the Summer of 2009, a
pushbroom VNIR/SWIR hyperspectral sensor collected data over a forested region of the Naval Surface Warfare Center,
Dahlgren Division, Virginia. This forested region can be best described as single canopy cover with multiple tree
species. Hyperspectral imagery was collected over multiple days and at multiple altitudes in August and September,
2009. On the ground, densiometer measurements and hemispherical photography were used to estimate canopy closure
at 10 meter intervals across a 2500 m<sup>2</sup> grid. Several spectral detection methods including vegetation indices, matched
filtering, linear un-mixing, and distance measures, are used to calculate canopy coverage at varying ground sample
distances and across multiple days. These multiple estimates are compared to the ground based measurements of canopy
closure. Results indicate that estimates of canopy coverage via VNIR/SWIR hyperspectral imagery compare well to the
ground based canopy closure estimates for this single canopy region. This would lead to the conclusion that it is possible
to use airborne VNIR/SWIR hyperspectral alone to provide an accurate estimate of canopy cover.
Visidyne has long been active in using ultra-high resolution, at the sub-picometer level optical interferometry to measure physical parameters as: strains, electric fields, and refractive index changes. With support from DARPA-SPO this capability was applied to developing and demonstrating an optics, photonics based magnetometer to detect small magnetic, B-fields associated with underground activities. The motivation for the effort came from the availability of high-activity magneto-optic (MO) materials, crystals that produces large path differences between states of polarization with an applied vector magnetic field, the Faraday effect. These crystals based on e.g., Yttrium Iron Garnets (YIG) were originally developed to serve as in-line isolators or diodes to reduce feedback in laser diode powered fiber optic communication links. Using these crystals, combined with high resolution interferometry allowed us to demonstrate a magnetic field or B-field sensor that in many ways is superior to existing magnetometer concepts, optics based or otherwise, in terms of sensitivity, bandwidth and dynamic range. Small size and low power requirements are features of the sensor.
The Geophysics Directorate of Phillips Laboratory has recently completed redesign of a heterodyne CO<SUB>2</SUB> differential absorption lidar which can simultaneously measure range resolved radial velocity, aerosol backscatter, and differential absorption. The transportable system utilizes two CO<SUB>2</SUB> transversely excited atmospheric (TEA) lasers which can be discretely tuned to many of the rotational lines compromising the 00 degree 1 to 10 degrees 0 vibrational bands of CO<SUB>2</SUB>. These lines span a spectral region from about 9.2 to 10.8 micrometers and allow for the DIAL measurement of some minor atmospheric molecular constituents as well as many anthropogenic organic species which have absorption bands in this spectral region. Transmission and reception is coaxial via a single shared 12 inch telescope and hemispherical scanner. Complete spectral processing of the heterodyne signals provides not only backscatter and differential absorption information but also radial wind velocity. Each TEA laser produces a line dependent pulse energy of 20-80 mJ at up to 150 Hz. Presently, the system is processor limited to a net pulse rate of 140 Hz. Results shown will include time-height cross-sections of cirrus backscatter, comparisons of CO<SUB>2</SUB> DIAL-derived water vapor profiles with simultaneous surface and radiosonde in-situ measurements, and wind velocity profiles in the troposphere.
A series of three-second firings of Space Shuttle Orbiter's 870-lbf Primary Reaction Control System thruster motors were photographed from the crew cabin with an intensified video camera. The spectral imager sequentially recorded 4 ms exposures at 30 Hz in six 20 to 30 nm FWHM channels centered from 400 to 800 nm, chosen specifically to study bi- propellant (monomethyl hydrazine fuel/nitrogen dioxide oxidizer) thruster exhaust chemistry. The species producing the visible radiance were earlier identified as CN, CH, C<SUB>2</SUB>, NO<SUB>2</SUB>, and HNO; the electronic bands originating from the same excited states of CN (B-X) and CH (A-X) extend into the near UV. Images of the vacuum core viewing within a few degrees of perpendicular to the first several meters from the exit plane were analyzed to relate the spatial distribution of exhaust product species and afterburning chemistry to a flowfield-kinetics model. Profiles of radiance transverse to the exhaust symmetry-axis show substantial limb brightening in all six channels, indicating that the distribution of the radiating species corresponds to a `zone'-type model of liquid-fuel film-cooled engine performance. Profiles of band radiance along the axis indicate the production and quenching of excited species as the exhaust gas adiabatically expands and cools.
Results of an analysis of intensified video photographs of a twilight venting of excess water from Space Shuttle are presented. The particle sizes, densities, and temperatures derived from the visible data are applied in estimating UV and IR radiances of the ice/vapor-containing volumes near Shuttle Orbiter, using a recently developed gas-transport/excitation model. The mean radius of the fragmentation-product droplets is 0.13 +/- 0.02 cm. This radius decreases by less than 5 percent over a 2.5-km initial flight path, and these particles survive for several hr. In the UV, intensities of radiation from the fragmentation particles fall off with decreasing wavelength due to the decrease in spectral irradiance of sunlight. In the IR, the mm particles are optically thick, while ice particles not greater than 0.3 micron are inefficient scatterer-radiators, except near 2.7 microns. The large-droplet component thus dominates the radiances even in projections to distant sensors, suppressing the severe spectral structure characteristic of the small droplets.