The performance of an optical system depends on the characteristics manufacturing errors of the mirrors, including aberrations on the primary mirror. When designing a system and evaluating its expected performance, the exact nature of the aberrations is not known beforehand, so approximations and simplifying assumptions need to be made. A common assumption is that aberrations of the primary mirror take the form of correlated Gaussian peaks and valleys about the ideal (perfectly spherical) primary mirror. The effect of such correlated Gaussian imperfections can be calculated in an average sense, using the optical quality factor (OQF) to modify the diffraction-limited modulation transfer function (MTF). Alternatively, a single instantiation of the aberrations can be added as phase variations to the pupil function, followed by calculation of the MTF. In this paper we compare these two methods of modeling the effects of correlated Gaussian aberrations on the MTF and point spread function (PSF). We explore the parameter space within which the OQF approximation is valid and the range of possible MTFs resulting from individual instantiations of the aberrations.
The remote sensing system engineering process often makes use of modeling and simulation tools to flow down specifications to subsystems and components, and/or to predict performance given a particular set of defined capabilities. A persistent question in the development and use of such tools is that of appropriate level of fidelity. In this paper we look at one problem area encountered in the simulation of panchromatic and other broadband imaging systems, that of accounting for spectrally varying resolution over the band. An established method for treating this variation is that of the polychromatic optical transfer function (OTF), but this technique imposes a measure of complexity on the simulation tool software architecture, as well as on users who must subsequently interact with it. We present a methodology for assessing the required level of fidelity for this problem and show that under some conditions it appears possible to forgo the polychromatic OTF formalism, or else to treat it with less than full rigor, with minimal loss in accuracy.
In a previous paper in this series, we described how The Aerospace Corporation's Parameterized Image Chain Analysis
& Simulation SOftware (PICASSO) tool may be used to model space and airborne imaging systems operating in the
visible to near-infrared (VISNIR). PICASSO is a systems-level tool, representative of a class of such tools used
throughout the remote sensing community. It is capable of modeling systems over a wide range of fidelity, anywhere
from conceptual design level (where it can serve as an integral part of the systems engineering process) to as-built
hardware (where it can serve as part of the verification process). In the present paper, we extend the discussion of
PICASSO to the modeling of Thermal Infrared (TIR) remote sensing systems, presenting the equations and methods
necessary to modeling in that regime.
In an earlier paper [Cota et al., Proc. SPIE 7087, 1-31 (2008)] we described how The Aerospace Corporation's
Parameterized Image Chain Analysis & Simulation SOftware (PICASSO) may be used with a reflectance calibrated
input scene, in conjunction with a limited number of runs of AFRL's MODTRAN4 radiative transfer code, to quickly
predict the top-of-atmosphere (TOA) radiance received by an earth viewing sensor, for any arbitrary combination of
solar and sensor elevation angles. In the present paper, we extend the method to the short and midwave IR, where
reflected solar and emitted thermal radiation both contribute to the TOA radiance received by a downlooking sensor.
In a companion paper presented at this conference we described how The Aerospace Corporation's Parameterized
Image Chain Analysis & Simulation SOftware (PICASSO) may be used in conjunction with a limited number of runs
of AFRL's MODTRAN4 radiative transfer code, to quickly predict the top-of-atmosphere (TOA) radiance received
in the visible through midwave IR (MWIR) by an earth viewing sensor, for any arbitrary combination of solar and
sensor elevation angles. The method is particularly useful for large-scale scene simulations where each pixel could
have a unique value of reflectance/emissivity and temperature, making the run-time required for direct prediction via
MODTRAN4 prohibitive. In order to be self-consistent, the method described requires an atmospheric model
(defined, at a minimum, as a set of vertical temperature, pressure and water vapor profiles) that is consistent with the
average scene temperature. MODTRAN4 provides only six model atmospheres, ranging from sub-arctic winter to
tropical conditions - too few to cover with sufficient temperature resolution the full range of average scene
temperatures that might be of interest. Model atmospheres consistent with intermediate temperature values can be
difficult to come by, and in any event, their use would be too cumbersome for use in trade studies involving a large
number of average scene temperatures. In this paper we describe and assess a method for predicting TOA radiance
for any arbitrary average scene temperature, starting from only a limited number of model atmospheres.
The design of any modern imaging system is the end result of many trade studies, each seeking to optimize image quality within real world constraints such as cost, schedule and overall risk. Image chain analysis - the prediction of image quality from fundamental design parameters - is an important part of this design process. At The Aerospace Corporation we have been using a variety of image chain analysis tools for many years, the Parameterized Image Chain Analysis & Simulation SOftware (PICASSO) among them. In this paper we describe our PICASSO tool, showing how, starting with a high quality input image and hypothetical design descriptions representative of the current state of the art in commercial imaging satellites, PICASSO can generate standard metrics of image quality in support of the decision processes of designers and program managers alike.
In this paper we model sub-pixel image registration for a generic earth-observing satellite system with a focal plane using two offset time delay and integrate (TDI) arrays in the focal plane to improve the achievable ground resolution over the resolution achievable with a single array. The modeling process starts with a high-resolution image as ground truth. The Parameterized Image Chain Analysis & Simulation Software (PICASSO) modeling tool is used to degrade the images to match the optical transfer function, sampling, and noise characteristics of the target system. The model outputs a pair of images with a separation close to the nominal half-pixel separation between the overlapped arrays. A registration estimation algorithm is used to measure the offset for image reconstruction. The two images are aligned and summed on a grid with twice the capture resolution. We compare the resolution in images between the inputs before overlap, the reconstructed image, and a simulation for the image which would have been captured on a focal plane with twice the resolution. We find the performance to always be better than the lower resolution baseline, and to approach the performance of the high-resolution array in the ideal case. We show that the overlapped array imager significantly outperforms both the conventional high- and low-resolution imagers in conditions with high image smear.
The design of any modern imaging system is the end result of many trade studies, each seeking to optimize image
quality within real world constraints such as cost, schedule and overall risk. The National Imagery Interpretability Rating
Scale (NIIRS) is a useful measure of image quality, because, by characterizing the overall interpretability of an image, it
combines into one metric those contributors to image quality to which a human interpreter is most sensitive. The main
drawback to using a NIIRS rating as a measure of image quality in engineering trade studies is the fact that it is tied to
the human observer and cannot be predicted from physical principles and engineering parameters alone. The General
Image Quality Equation (GIQE) of Leachtenauer et al. 1997 [Appl. Opt. 36, 8322-8328 (1997)] is a regression of actual
image analyst NIIRS ratings vs. readily calculable engineering metrics, and provides a mechanism for using the expected
NIIRS rating of an imaging system in the design and evaluation process. In this paper, we will discuss how we use the
GIQE in conjunction with The Aerospace Corporation's Parameterized Image Chain Analysis & Simulation SOftware
(PICASSO) to evaluate imager designs, taking a hypothetical high resolution commercial imaging system as an example.
The design of any modern imaging system is the end result of many trade studies, each seeking to optimize image
quality within real world constraints such as cost, schedule and overall risk. Image chain analysis - the prediction of
image quality from fundamental design parameters - is an important part of this design process. At The Aerospace
Corporation we have been using a variety of image chain analysis tools for many years, the Parameterized Image Chain
Analysis & Simulation SOftware (PICASSO) among them. In this paper we describe our PICASSO tool, showing how,
starting with a high quality input image and hypothetical design descriptions representative of the current state of the art
in commercial imaging satellites, PICASSO can generate standard metrics of image quality in support of the decision
processes of designers and program managers alike.
In this paper we model sub-pixel image registration for a generic earth-observing satellite system with a focal plane
using two offset Time Delay and Integrate (TDI) arrays in the focal plane to improve the achievable ground resolution
over the resolution achievable with a single array. The modeling process starts with a high-resolution image as ground
truth. The Parameterized Image Chain Analysis & Simulation SOftware (PICASSO) modeling tool is used to degrade
the images to match the optical transfer function, sampling, and noise characteristics of the target system. The model
outputs a pair of images with a separation close to the nominal half-pixel separation between the overlapped arrays. A
registration estimation algorithm is used to measure the offset for image reconstruction. The two images are aligned and
summed on a grid with twice the capture resolution. We compare the resolution in images between the inputs before
overlap, the reconstructed image, and a simulation for the image which would have been captured on a focal plane with
twice the resolution. We find the performance to always be better than the lower resolution baseline, and to approach
the performance of the high-resolution array in the ideal case. We show that the overlapped array imager significantly
outperforms both the conventional high- and low-resolution imagers in conditions with high image smear.
A new era in atmospheric remote sensing will begin with the launch of the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Preparatory Project (NPP) spacecraft in 2006, and the multiple operational NPOESS launches in sun-synchronous orbital planes (nominally 13:30, 17:30, or 21:30 local equatorial crossing times) starting in 2009. Cloud and atmosphere polar-orbiting environmental satellite data will be profoundly improved in radiometric quality, spectral coverage, and spatial resolution relative to current operational civilian and military polar-orbiting systems. The NPOESS Visible Infrared Imaging Radiometer Suite (VIIRS) will provide Environmental Data Records (EDRs) for day and night atmosphere and cloud operational requirements, as well as sea surface temperature (SST) and many important land EDRs by ground processing of raw data records (RDRs) from the VIIRS sensor. VIIRS will replace three currently operating sensors: the Defense Meteorological Satellite Program (DMSP) Operational Line-scanning System (OLS), the NOAA Polar-orbiting Operational Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR), and the NASA Earth Observing System (EOS Terra and Aqua) MODerate-resolution Imaging Spectroradiometer (MODIS). This paper describes the VIIRS all-reflective 22-band single-sensor design, following the Critical Design Review (CDR) in Spring 2002. VIIRS provides low noise (driven by ocean color for the reflective visible and near-IR spectral bands and by SST for the emissive mid and long-wave IR spectral bands), excellent calibration and stability (driven by atmospheric aerosol and cloud EDRs, as well as SST), broad spectral coverage, and fine spatial resolution driven by the cloud imagery EDR. In addition to improved radiometric, spectral, and spatial performance, VIIRS features DMSP OLS-like near-constant resolution, global twice-daily coverage in each orbit plane, and direct heritage to proven design innovations from the successful Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Earth Observing System (Terra and Aqua) MODIS.
This paper presents an overview of the Visible and Infrared Imaging Radiometer Suite (VIIRS) design process that achieved exceptional competitive IPO ratings for system optimization, sensor system design, and systems engineering, integration and test (SEIT). A novel aspect of the competition was provision to the sensor competitors of a specification of geophysical measurement requirements called Environmental Data Records (EDRs), rather than a sensor hardware specification. The contractors were required to derive optimal VIIRS hardware specifications from the EDRs and Raytheon's process is the subject of this paper. VIIRS will become the next-generation United States polar-orbiting Operational Environmental Satellite System (MPOESS) Preparatory Project (NPP) spacecraft. Beginning in 2008, the NPOESS VIIRS instrument will be launched into 1370, 1730, and 2130 local-time ascending-node sun-synchronous polar orbits as the single operational source for dozens of civil and defense environmental and weather products, as well as climate research data. VIIRS will replace three different currently operating sensors: the Defense Meteorological Satellite Program (DMSP) Operational Line-scan System (OLS), the NOAA Polar-orbiting Operational Environmental Satellite (POES) Advanced Very High Resolution Radiometer (AVHRR), and the NASA Earth Observing System (EOS Terra and Aqua) MODerate-resolution Imaging Spectroradiometer (MODIS). A critical VIIRS challenge was design optimization to differing requirements from the three user agencies (DoD, NOAA, and NASA) represented by the NPOESS Integrated Program Office.
KEYWORDS: Sensors, Image processing, Signal to noise ratio, Digital filtering, Signal processing, Systems modeling, Imaging systems, Target detection, Analog filtering, Point spread functions
This paper provides an overview of an advanced simulation capability currently in use for analyzing visible and infrared sensor systems. The software system, called VISTAS (VISIBLE/INFRARED SENSOR TRADES, ANALYSES, AND SIMULATIONS) combines classical image processing techniques with detailed sensor models to produce static and time dependent simulations of a variety of sensor systems including imaging, tracking, and point target detection systems. Systems modelled to date include space-based scanning line-array sensors as well as staring 2-dimensional array sensors which can be used for either imaging or point source detection.
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.