The FITTS correlation algorithm has been widely used for over forty years in high speed video trackers. It has the advantage that it is very simple implement in a digital processor with a small number of calculations. At each step the algorithm attempts to estimate the shift between an image of a moving target and a proto-type image. There are several well-known short comings of the FITTS algorithm. First the error in the shift estimate increases if the shift is greater than one pixel of the digital image. Secondly all correlation based tracking algorithms are susceptible to low frequency drift. These errors can force a lower tracker closed loop bandwidth to maintain track loop stability. In this paper we examine in an intuitive manner the underlying cause of the drift and approaches to its mitigation.
KEYWORDS: Detection and tracking algorithms, Video, Fourier transforms, Sensors, Error analysis, Signal to noise ratio, Image filtering, Phase only filters, Digital imaging, Interference (communication)
The FITTS correlation algorithm has been widely used for over forty years in high speed video trackers. It has the advantage that it is very simply implemented in a digital computer with a small number of calculations. At each step the algorithm attempts to estimate the shift between an image of a moving target and a proto-type image. There are several well-known short comings of the FITTS algorithm. First the error in the shift estimate increases if the shift is greater than one pixel of the digital image. Second the FITTS algorithm is susceptible to errors from sensor noise if the video images have low signal to noise ratio. These errors can force a lower tracker closed loop bandwidth to maintain track loop stability. An alternative correlation tracker algorithm is known as Projection Based Phase Only Correlation. In this paper we compare the two algorithms with respect to the effect of sensor noise.
Laser Aided Detection and Ranging (LADAR) imaging systems can be used to provide high resolution
imaging and tracking of moving targets at night. Central to the tracking system is a high speed correlation
algorithm to determine target motion between sensor image frames. Several issues complicate the
correlation calculations. These include coherent speckle noise and atmosphere induced scintillation of the
illuminator beam. The Fitts correlation algorithm is commonly used because of its simplicity and speed.
However it is only optimal when the shift between sensor frames is less than a pixel. In addition it can be
sensitive to certain types of noise. Projection based phase only (PBPO) is another type of correlation
algorithm that is also high speed and in many cases less sensitive to noise. In this paper we compare the
Fitts algorithm with PBPO in terms of number of computations and noise immunity when used in a
LADAR tracker.
The Standoff Intelligence Detection (SID) program is an Air Force Research Laboratory (AFRL) quick reaction program, tasked with providing the warfighter ready-now technologies related to directed energy, optics, and photonics. The first variant of these aircraft was started in 2008 utilizing two Cessna 182Q aircraft retrofitted with a
wing mounted imaging systems and mission equipment. The 3rd generation of these imaging aircraft is equipped on a Cessna T-206H, Turbo Stationair. The aircraft is a 6-seat, single-engine aircraft, retrofitted with an MX-15HDi sensor system and supporting equipment.
The SID Program has produced the aircraft to provide an ISR platform to support tests, exercises, search and rescue, and real-world needs.
Laser aided detection and ranging (LADAR) imaging systems are usually corrupted by several pathologic
noises. Speckle noise is due to the coherent nature of the laser illuminator. Scintillation noise is introduced
by atmospheric turbulence over the outgoing illumination path and manifests itself as a multiplicative noise
in the imagery. These noises can be mitigated by a simple recursive averaging algorithm when looking at
fixed targets in staring mode. However if the target under observation is moving with respect to the
imaging platform, the averaging will cause the target image to smear. In such a case, a maximum a-posteriori
(MAP) approach can be used to estimate localized statistics of the scene under observation as
well as the scintillation. The parameter estimates can then be incorporated into a spatially and temporally
adaptive averaging approach which mitigates the noise while at the same time preserving motion in the
scene.
Recent advances in InGaAs camera technology has stimulated interest in the short wave infra-red (SWIR) band in
the spectral region 0.84 – 1.7 μm. Located between the visible and thermal infra-red, the SWIR band shows
interesting properties of both. Images tends to have the look of the visible and are less affected by scattering from
aerosol haze, however the solar irradiance is dropping rapidly with wavelength in the SWIR. Spectral signatures,
particularly of paints and dyes, may be different in the SWIR band compared to the visible. For these reasons we
have chosen to investigate hyper-spectral measurements in this band using the NovaSol μHSI SWIR hyper-spectral
imager system.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band with
wavelength between 0.9 and 1.7 μm. This air glow has been proposed as an illumination source for obtaining
imagery in the dark of night. By examining short term nightly fluctuations and long term seasonal trends in the
ground level irradiance we hope to determine the source reliability for night time low light surveillance and imaging.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between
0.9 and 1.7 μm wave length. This phenomenon, often referred to as airglow, has been demonstrated as an effective
illumination source for passive low light level night time imaging applications. It addition it has been shown that
observation of the spatial and temporal variations of the illumination can be used to characterize atmospheric tidal
wave actions in the airglow region. These spatio-temporal variations manifest themselves as traveling wave
patterns whose period and velocity are related to the wind velocity at 85 km as well as the turbulence induced by
atmospheric vertical instabilities. In this paper we present nearly a year of airglow observations over the whole
sky, showing long term and short term fluctuations to characterize SWIR night time image system performance.
Intensity interferometery holds tremendous potential for remote sensing of space objects. Whereas spatial
resolution of imagery obtained from earth-based observatories is typically limited by both the size of the
primary mirror and atmospheric effects, intensity interferometers (IIs) are relatively unaffected by
atmospheric distortions and their effective apertures can be substantially larger than is practical for
traditional observatories. Most intensity interferometer measurements have been performed in the visible
region due to well-known issues of poor signal to noise ratios and the performance of detectors in the
visible spectral bands. In fact the short-wave infrared (SWIR) spectral band is relatively unexplored for II
applications. In this paper we investigate the measurement signal to noise terms for a notional SWIR
intensity interferometer. Our study goes beyond the most basic SNR equations of II, and analyzes
atmospheric effects, sky backgrounds, and detector characteristics, considering the current state-of-the-art
for experiments in the short-wave infrared spectral region.
Recent advances in InGaAs camera technology has stimulated interest in the short wave infra-red (SWIR) band in
the spectral region 0.9 - 1.7 μm. Located between the visible and thermal infra-red, the SWIR band shows
interesting properties of both. Images tends to have the look of the visible and are less affected by scattering from
aerosol haze, however the solar irradiance is dropping rapidly with wavelength in the SWIR. Spectral signatures,
particularly of paints and dyes, may be different in the SWIR band compared to the visible. For these reasons we
have chosen to investigate hyper-spectral measurements in this band using the NovaSol μHSI SWIR hyper-spectral
imager system.
Airglow luminescence in the SWIR region due to upper atmospheric recombination of solar excited molecules is a
well accepted phenomenon. While the intensity appears broadly uniform over the whole sky hemisphere, we are
interested in variations in four areas: 1) fine periodic features known as gravity waves, 2) broad patterns across the
whole sky, 3) temporal variations in the hemispheric mean irradiance over the course of the night, and 4) long term
seasonal variations in the mean irradiance. An experiment is described and results presented covering a full year of
high resolution hemispheric SWIR irradiance images. An automated gimbal views 45 hemispheric positions, using
30 second durations, and repeats approximately every half hour through out the night. The gimbal holds co-mounted
and bore-sighted visible and SWIR cameras. Measuring airglow with respect to spatial, temporal, and seasonal
variations will facilitate understanding its behavior and possible benefits, such as night vision and predicting upper
atmosphere turbulence. The measurements were performed in a tropical marine location on the island of Kauai Hi.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between
0.9 and 1.7 μm wave length. This phenomenon, often referred to as airglow, has been demonstrated as an effective
illumination source for passive low light level night time imaging applications. It addition it has been shown that
observation of the spatial and temporal variations of the illumination can be used to characterize atmospheric tidal
wave actions in the airglow region. These spatio-temporal variations manifest themselves as traveling wave
patterns whose period and velocity are related to the wind velocity at 85 km as well as the turbulence induced by
atmospheric vertical instabilities. In this paper we present nearly a year of airglow observations over the whole
sky, showing long term and short term fluctuations to characterize SWIR night time image system performance.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band with
wavelength between 0.9 and 1.7 μm. By examining images in an urban and a rural setting, we investigate the
correlation between the appearances of passive dark of night images in the SWIR with NIR- visible. The
experimental setup consists of two sensors, a NIR-visible CCD and an InGaAs array sensitive in the SWIR, both colocated
on an AZ-EL mount, and both co-boresighted so that different viewing angles of the sky and terrestrial
scenes are possible. By making corrections for focal length and pixel size, the visible and SWIR data can be
compared. After taking several nights of data in the urban environment of Albuquerque, NM, the entire system was
then re-located to a rural location on the island of Kauai in a rural setting with very low ambient light. It is shown
that under most conditions the SWIR sensor produces significantly better imagery using the airglow illumination
source.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between
0.9 and 1.7 μm wave length. This has been demonstrated as an effective illumination source for night time imaging
applications. It addition it has been shown that observation of the spatial and temporal variations of the
illumination can be used to characterize atmospheric tidal wave actions in the air glow region. These spatiotemporal
variations manifest themselves as traveling wave patterns whose period and velocity are related to the
wind velocity at 85 km as well as the turbulence induced by atmospheric vertical instabilities. We are interested in
studying these phenomena for a variety of reasons. First they can give an insight into upper atmospheric physics,
second we would like to understand the variations in order to determine if air glow can be used as a reliable
illumination source for night time terrestrial imaging. To that end we have been collecting data on ground
irradiance from air glow over the past six months at a site on the island of Kauai. The purpose of this paper is to
discuss some initial analysis of this data.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band of wave
length 0.9 to 1.7 μm. Numerous studies of these phenomena have demonstrated that the irradiance shows significant
temporal and spatial variations in the night sky. Changes in weather patterns, seasons, sun angle, moonlight, etc
have the propensity to alter the SWIR air glow irradiance pattern. By performing multiple SWIR measurements a
mosaic representation of the celestial hemisphere was constructed and used to investigate these variations over time
and space. The experimental setup consisted of two sensors, an InGaAs SWIR detector and a visible astronomical
camera, co-located and bore sighted on an AZ-EL gimbal. This gimbal was programmed to view most of the sky
using forty five discrete azimuth and elevation locations. The dwell time at each location was 30 seconds with a
total cycle time of less than 30 minutes. The visible astronomical camera collected image data simultaneous with
the SWIR camera in order to distinguish SWIR patterns from clouds. Data was reduced through batch processing
producing polar representations of the sky irradiance as a function of azimuth, elevation, and time. These spatiotemporal
variations in the irradiance, both short and long term, can be used to validate and calibrate physical models
of atmospheric chemistry and turbulence. In this paper we describe our experimental setup and present some results
of our measurements made over several months in a rural marine environment on the Island of Kauai Hawaii.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band between
0.9 and 1.7 μm wave length. This has been demonstrated as an effective illumination source for night time imaging
applications. It addition it has been shown that observation of the spatial and temporal variations of the
illumination can be used to characterize atmospheric tidal wave actions in the sky glow region. These spatiotemporal
variations manifest themselves as traveling wave patterns whose period and velocity are related to the
wind velocity at 85 km as well as the turbulence induced by atmospheric vertical instabilities. Ground to space
observation systems especially those employing adaptive optics are adversely affected by high altitude turbulence
and winds. In this paper we propose the use of sky glow observations to predict and characterize image system
degradation due to upper atmosphere turbulence.
It is well known that luminance from photo-chemical reactions of hydroxyl ions in the upper atmosphere (~85 km
altitude) produces a significant amount of night time radiation in the short wave infra-red (SWIR) band of wave
length 0.9 to 1.7 μm. Numerous studies of these phenomena have demonstrated that the irradiance shows significant
temporal and spatial variations in the night sky. Changes in weather patterns, seasons, sun angle, moonlight, etc
have the propensity to alter the SWIR air glow irradiance pattern. By performing multiple SWIR measurements a
mosaic representation of the celestial hemisphere was constructed and used to investigate these variations over time
and space. The experimental setup consisted of two sensors, an InGaAs SWIR detector and a visible astronomical
camera, co-located and bore sighted on an AZ-EL gimbal. This gimbal was programmed to view most of the sky
using forty five discrete azimuth and elevation locations. The dwell time at each location was 30 seconds with a
total cycle time of less than 30 minutes. The visible astronomical camera collected image data simultaneous with
the SWIR camera in order to distinguish SWIR patterns from clouds. Data was reduced through batch processing
producing polar representations of the sky irradiance as a function of azimuth, elevation, and time. These spatiotemporal
variations in the irradiance, both short and long term, can be used to validate and calibrate physical models
of atmospheric chemistry and turbulence. In this paper we describe our experimental setup and present some results
of our measurements made over several months in a rural marine environment on the Islands of Kauai and Maui
Hawaii.
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