In: Wagner W., Székely, B. (eds.): ISPRS TC VII Symposium - 100 Years ISPRS, Vienna, Austria, July 5-7, 2010, IAPRS, Vol. XXXVIII, Part 7B
THE ADVANTAGES OF BORESIGHT EFFECTS IN THE HYPERSPECTRAL DATA
ANALYSIS
Anna Brook, Eyal Ben-Dor
Remote Sensing Laboratory, Tel-Aviv University, Israel
anna.brook@gmail.com
Commission VI, WG VI/4
KEY WORDS: Bore Sight, Dual pushbroom line-based hyperspectral sensors, Shadow Map, Stereo 3-D Map, Anomaly Detection
ABSTRACT:
The Dual push-broom line-based hyperspectral sensors combine two different instruments that are usually mount on the same
optical bench. This configuration leads to problems such as co-registration of pixels and squint of the field of view known as
boresight effect. Image orientation parameters and sensor boresight of any sensor during data acquisition became possible by a
combination of an inertial measurement system (IMU) and GPS. The different position of the IMU, the GPS antenna and the
imaging sensors, causes an orientation and boresight effect. Any small change in the correction of internal orientation affects the co
registration between VNIR and SWIR region of hyperspectral images. Correcting the boresight effect is an almost automatically key
mission taken by all Dual system users. This is because the boresight effect is considered as a noise in the system and a problem that
needs to be corrected prior to any data analysis. We propose to use the boresight effect as a vehicle to monitor and detect some
spectral phenomena in the image that can't be obtained in corrected images. The advantage of the sensors orientation and boresight
effect was investigated based on the AISA-Dual sensor that combines EAGLE for the VIS-NIR (400-970nm) and HAWK for the
SWIR (980-2450nm). An experience of more than six years with this sensor, we have found that the boresight effect have some
positive outcomes on the analysis results of the hyperspectral remote sensing (HRS) data. This led us to generate an HRS processing
protocol where this effect is examined for gaining the most from the data. Three applications were investigated as follow: 1)
enhancing shadowing effect, 2) generating a 3-D view, and 3) performing a better detection of boarder anomaly. We will
demonstrate these three options and suggest a possible use of this idea from orbit.
1. INTRODUCTION
Hyperspectral imaging spectrometers produce data with
high spectral resolution (in the range of 5 to 15 nm) and
continues band configuration, giving processors the ability to
detect subtle spectra features and defined chemical and
physical properties of the sensed objects. This powerful
capability is important for remote sensing applications e.g.
geologic typing and surveying, agricultural monitoring and
optimization, environmental damage assessment, forestry
surveys, detection of man-made materials, etc.
The determination of image orientation parameters of any
sensor during data acquisition became possible by combined
use of an inertial measurement unit (IMU) and GPS. In this
integrated system, GPS antenna, IMU and imaging sensor are
located different position in airborne carrier. Because of this
reason, the displacement vectors between sensors have to be
determined. Similarly, axes of the IMU and imaging sensor are
not same and a miss-orientation matrix exists between them.
System calibration is including both calibration of individual
sensor and calibration between sensors. The IMU calibration for
drifts and biases and the calibration of imaging sensor for
interior orientation parameter are components of sensor
calibration. Calibration between sensors contains the
determination of a constant displacement vector between
sensors and a constant miss-orientation matrix between IMU
body frame and imaging sensor frame. The boresight
misalignment, the relation between the IMU and the imaging
sensor is determined by bundle block adjustment using a
calibration flight. The small change of correction of interior
orientation affects co-registration between sensors and thus
hyperspectral images of VNIR and SWIR region. The
processing step that can be applied to the data is
georectification that collects generated (VNIR and SWIR)
imagery and navigation data and automatically geo-locate and
rectify pixel-by-pixel the image data.
AISA-Dual is an airborne imaging spectrometer designed
by Specim LTD, as a research sensor that capable of producing
medial to high fidelity hyperspectral remote sensing (HRS) data
in the 400 to 2400 nm wavelength range. The system consists of
a sensor head, containing a pair of co-boresighted grating
spectrometers (VIS-NIR sensor EAGLE and SWIR sensor
HAWK), two electronics racks, and a digital data recorder. It
simultaneously acquires images in 198 contiguous spectral
bands with spectral resolution in the range of 12nm in VNIR
region, and 6nm in SWIR region. Each spectrometer consists of
a set of refractive foreoptics that image the scene onto a slit.
Light passing through the slit is dispersed perpendicular to the
slit by a flat rating and then imaged onto a 2-D focal plane
array. One dimension of the array along the slit provides spatial
scene information. The second dimension of the array, along
which the light from any given point in the slit has been
dispersed, provides spectral information. An image is generated
by moving the instrument across a scene in a push-broom
fashion, perpendicularly to the instrument’s slits, and recording
frames of spectral and spatial information detected by the VNIR
and SWIR. The system is usually operated on aircraft at altitude
of 10,000 ft that together with instant field of view (IFOV) of 1
mrad provides a spatial resolution of 1.5 m. A standard AISA-
Dual data set is a 3-D data cube in non-earth coordinate system.
It has 286 pixels in the cross-track and hundreds of pixels in the
along-track direction. The top-level performance requirements
were for an instrument with fair signal to noise ratio (SNR), co
registered spectral bands taken simultaneously by different
detectors, accurate location for each pixel, and accurate
radiometric calibration.
* Anna Brook, the Remote and GIS Sensing Laboratory, Tel-Aviv University. Ramat Aviv P.O. Box 39040 Tel Aviv 69978, Israel,
Tel: 972-3-6407049 Fax: 972-3-6406243 Email: anna.brook@gmail.com.
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