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The Suomi-NPP Visible Infrared Imager Radiometer Suite (VIIRS) instrument provides the next generation of visible/infrared imaging including the day/night band (DNB) with nominal bandwidth from 500 to 900 nm. Previous to VIIRS, the Defense Meteorological Satellite Program Operational Linescan System (OLS) measured radiances that spanned over seven orders of magnitude, using an onboard gain adjustment to provide the capability to image atmospheric features across the solar terminator, to observe nighttime light emissions over the globe, and to monitor the global distribution of clouds. The VIIRS DNB detects radiances that span over eight orders of magnitude, and because it has 13–14-b quantization (compared with 6 b for OLS) with three gain stages, the DNB has its full dynamic range at every part of the scan. One process that is applied to the VIIRS DNB radiances is a solar/lunar zenith angle dependent gain adjustment to create near-constant contrast (NCC) imagery. The at-launch NCC algorithm was designed to reproduce the OLS capability and, thus, was constrained to solar and lunar angles from 0 $^{\circ}$ to 105 $^{\circ}$ . This limitation has, in part, lead to suboptimal imagery due to the assumption that DNB radiances fall off exponentially beyond twilight. The VIIRS DNB ultrasensitivity in low-light conditions enables it to detect faint emissions from a phenomenon called airglow, thus invalidating the exponential fall-off assumption. Another complication to the NCC imagery algorithm is the stray light contamination that contaminates the DNB radiances in the astronomical twilight region. We address these issues and develop a solution that leads to high-quality imagery for all solar and lunar conditions.

[1] The Suomi National Polar-Orbiting Partnership (NPP) launched on 28 October 2011 hosts the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor. The VIIRS sensor includes a day-night band (DNB) that covers almost 7 orders of magnitude in its dynamic range from full sunlit scenes to lunar-illuminated clouds. The DNB is panchromatic and covers the wavelengths from 500 nm to 900 nm. Since launch, extensive effort has gone into its characterization. We have shown that the DNB is performing extremely well, meeting most of its specifications with some minor exceedances. The DNB characteristics evaluated include the following: sampling and resolution across the swath, geolocation uncertainty, radiometric sensitivity, radiometric uncertainty, and stray light. The only significant deviation from specification involves the stray light specification. On-orbit, the characterization shows that the DNB suffers stray light level on the order of 100% Lmin or 3 × 10−9 W∙cm−2∙sr−1. After algorithmic correction, the residual radiometric error was reduced to approximately 4.5 × 10−10 W∙cm−2∙sr−1.

Fog and low visibility conditions have hampered aviation since its inception. Fog-related accidents are numerous, and canceled take-offs and landings due to fog and low visibility conditions (Cat III) have significant economic impact on airlines, parcel carriers and general aviation. Millimeter waves have good propagation properties in weather and give adequate spatial resolution when used to image the forward scene. Passive millimeter wave focal plane array cameras are new sensors which, integrated into future guidance and landing systems, promise to be an effective aid, or alternative, to existing technology for aircraft landings and take-offs under Cat III conditions. They can produce visual-like radiometric images at real time frame rates (up to 30 Hz), and are directly amenable to image fusion with infrared and visible images. TRW has been actively involved in developing and productizing this technology both at the hardware and the system levels. >

We have developed a concept for a high average power FEL which incorporates a superconducting rf linac in an energy recovery configuration to increase the overall efficiency. Our design minimizes space charge effects at low beam energy by using: (1) higher than usual voltages on our grid modulated electrostatic electron gun and (2) pulse widths much longer than usual, from the gun. These pulses are compressed a minimum amount at the superconducting accelerator, which contains cavities at both fundamental and third-harmonic frequencies to flatten the voltage gain over these long pulses. After acceleration to the full beam energy, the pulses are compressed further to produce the peak currents required for the design FEL conversion efficiency. To validate the concept, we have designed an experiment to produce the required beam, accelerate it to 5 MeV and then recirculate the beam to demonstrate the anticipated high recovery efficiency. The injector gun for this experiment has now been operated at its design voltage and the current and the beam characteristics measured (design specifications: 1 nC, 0.5 ns). The beam emittance (ϵn) over 90% of the beam profile has been determined for various accelerating gradients and is 8π mm mrad. The energy slewing cavity required for bunching the beam a factor of 3 is in fabrication, as is the superconducting 500 MHz accelerator cavity. A description of our injector system design and the latest superconducting accelerator cavity tests will be reported.

The Visible/Infrared Imager Radiometer Suite (VIIRS), built by Raytheon Santa Barbara Remote Sensing (SBRS) will be one of the primary earth-observing remote-sensing instruments on the National Polar-Orbiting Operational Environmental Satellite System (NPOESS). It will also be installed on the NPOESS Preparatory Project (NPP). These satellite systems fly in near-circular, sun-synchronous low-earth orbits at altitudes of approximately 830 km. VIIRS has 15 bands designed to measure reflectance with wavelengths between 412 nm and 2250 nm, and an additional 7 bands measuring primarily emissive radiance between 3700nm and 11450 nm. The calibration source for the reflective bands is a solar diffuser (SD) that is illuminated once per orbit as the satellite passes from the dark side to the light side of the earth near the poles. Sunlight enters VIIRS through an opening in the front of the instrument. An attenuation screen covers the opening, but other than this there are no other optical elements between the SD and the sun. The BRDF of the SD and the transmittance of the attenuation screen is measured pre-flight, and so with knowledge of the angles of incidence, the radiance of the sun can be computed and is used as a reference to produce calibrated reflectances and radiances. Unfortunately, the opening also allows a significant amount of reflected earthshine to illuminate part of the SD, and this component introduces radiometric error to the calibration process, referred to as earthshine contamination (ESC). The VIIRS radiometric error budget allocated a 0.3% error based on modeling of the ESC done by SBRS during the design phase. This model assumes that the earth has Lambertian BRDF with a maximum top-of-atmosphere albedo of 1. The Moderate Resolution Imaging Spectroradiometer (MODIS) has an SD with a design similar to VIIRS, and in 2003 the MODIS Science Team reported to Northrop Grumman Space Technology (NGST), the prime contractor for NPOESS, their suspicion that ESC was causing higher than expected radiometric error, and asked whether VIIRS might have a similar problem. The NPOESS Models and Simulation (M&S) team considered whether the Lambertian BRDF assumption would cause an underestimating of the ESC error. Particularly, snow, ice and water show very large BRDFs for geometries for forward scattered, near-grazing angles of incidence, and in common parlance this is called glare. The observed earth geometry during the period where the SD is illuminated by the sun has just such geometries that produce strongly forward scattering glare. In addition the SD acquisition occurs in the polar regions, where snow, ice and water are most prevalent. Using models in their Environmental Products Verification and Remote Sensing Testbed (EVEREST), the M&S team produced a model that meticulously traced the light rays from the attenuation screen to each detector and combined this with a model of the satellite orbit, with solar geometry and radiative transfer models that include the effect of the BRDF of various surfaces. This modeling showed that radiometric errors up to 4.5% over water and 1.5% over snow or ice. Clouds produce errors up to 0.8%. The likelihood of these high errors occurring has not been determined. Because of this analysis, various remedial options are now being considered.

The tri-agency Integrated Program Office (IPO) is managing the development of the National Polar-orbiting Operational Environmental Satellite System (NPOESS). Later this decade, the IPO, through its prime contractor, Northrop Grumman Space Technology (NGST), will launch NPOESS spacecraft into three orbital planes (1330, 1730, and 2130 equatorial ascending nodal crossing times) to provide global coverage with a data refresh rate of approximately four hours. A globally distributed ground system will deliver 95 percent of the data within 26 minutes from the time of on-orbit collection. With the development of NPOESS, we are evolving the existing “weather” satellites into integrated environmental observing systems. To meet user-validated requirements, NPOESS will deliver global data for 55 Environmental Data Records (EDRs). Performance characteristics and attributes have been defined for each of the 55 parameters, including: horizontal/vertical resolution; mapping accuracy; measurement range; measurement precision and uncertainty; refresh rate; data latency; and geographic coverage. Long-term stability requirements have been defined for key parameters to ensure temporal consistency and continuity of data over the operational life of NPOESS. The actual EDR performances will be a result of the sensor and algorithm performances. In order for NPOESS program to determine estimates of EDR performance based on current design data and to assess potential sensor design changes or algorithm modifications, NGST developed an Integrated Weather Products Test Bed (IWPTB). This system can generate simulated radiances from mission/orbit variable, sensor variables, atmospheric and background conditions, and radiative transfer models. These simulated radiances at aperture are used with sensor models and spacecraft factors to generate simulated radiometric temperatures which are processed by science retrieval code to generate EDRs. This paper presents an assessment of the impact of the VIIRS sensor design modification to correct Modulated Instrument Background in the sensor’s optical train. This assessment, which focuses on the Sea Surface Temperature EDR in particular, was generated by the IWPTB end-to-end performance assessment capability.

Passive millimeter wave (PMMW) focal plane array cameras are new sensors capable of imaging the forward scene under fog and low-visibility conditions at video frame rates. PMMW imaging sensors measure the blackbody radiation naturally emitted from the imaged scene. These cameras promise to be an effective aid, or an alternative, to existing technology for aircraft landing and surface operations under Category Ill weather conditions. The impact of this technology on air traffic can be significant in terms of reducing weather-related accidents and delays as well as affecting the economics of airlines, parcel carriers and general aviation. The authors discuss the system engineering necessary to validate the mission's operational requirements. The associated hardware development work is outlined. The suitability of PMMW cameras to future enhanced and synthetic vision systems is considered. >

Fog and low visibility conditions have hampered aviation since its inception. Fog-related accidents are numerous, and canceled take-offs and landings due to fog and low visibility conditions (Cat III) have significant economic impact on airlines, parcel carriers and general aviation. Millimeter waves have good propagation properties in weather and give adequate spatial resolution when used to image the forward scene. Passive millimeter wave focal plane array cameras are new sensors which, integrated into future guidance and landing systems, promise to be an effective aid, or alternative, to existing technology for aircraft landings and take-offs under Cat III conditions. They can produce visual-like radiometric images at real time frame rates (30 Hz), which can be directly fused with infrared and visible images. TRW has been actively involved in developing and manufacturing this technology both at the hardware and the system levels. >

The performance of passive microwave radiometers in detecting buried landmines is adversely affected by the presence of foreign objects and moisture in the soil. One possible way to increase the signal contrast between the mine and the surrounding soil is to make the soil artificially dry by reducing the moisture to its solid state. This can be accomplished by injecting liquid nitrogen into the top layers of the soil. This paper describes preliminary result of an experiment designed to test this approach under controlled laboratory conditions.

The concept of using passive microwave radiometers for the detection of buried objects is well rooted in the theory of radiation propagation through lossy media. As the dielectric discontinuity at the boundary layer between the foreign object and the soil cause a reflection of the incoming radiation,the object present different radiometric properties than the surrounding background, and becomes detectable as a change in the antenna temperature. Under a contract from the US Army's Night Vision and Electronics Sensors, TRW has designed and built two hand-held man- portable units, which employ the cold radiometric sky as the illuminating source. The units work at 1.7 and 5 GHz using direct RF-gain, total-power radiometers. The units were field-tested at the Army facility at Fort AP Hill during October of 1998. The test yielded a very exciting detection rate of 100 percent and a false alarm rate of 0.28/m 2 .

TRW has recently developed InP low noise amplifiers operating at 140 GHz. Similar to the evolution of 94 GHz GaAs technology, this lays the foundation for the development of a 140 GHz MMIC receiver for use in a next generation passive millimeter-wave video camera capable of generating a real time display of the imaged scene. The advantages of going to 140 GHz, and the use of InP technology, will be discussed.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A passive millimeter-wave (PMMW) camera capable of generating a real time display of the imaged scene, similar to video cameras, has been developed at TRW and is undergoing field testing. The camera operates at 89 GHz, acquiring images at a frame rate of 17 Hz. This work reports on the video imaging generated by the camera. This research is carried out under the Passive Millimeter-Wave Camera Consortium, a cost-shared program between the Defense Advanced Research Programs Agency and an industrial consortium that includes Honeywell, McDonnell Douglas and TRW. It is managed for the Department of Defense by NASA-LaRC.

Extending earlier successful radiometric detection of both metal and plastic mines, both buried and unburied at 44 and 12 GHz, a lower frequency radiometer was tested to determine its effectiveness under soil conditions of higher water content. In addition, the ability to generate 2D images was evaluated using a novel image processing technique, and the results were compared to model predictions.

In order to predict the performance of a passive millimeter wave sensor under a variety of weather, terrain and sensor operational conditions, TRW has developed the Advanced Radiometric Millimeter-Wave Scene Simulation (ARMSS) code. This code provides a comprehensive, end-to-end scene simulation capability based on rigorous, `first-principle' physics models of the passive millimeter wave phenomenology and sensor characteristics. The ARMSS code has been extensively benchmarked against both data in the literature and a wide array of millimeter-wave-field-imaging data. The code has been used in support of numerous passive millimeter wave technology programs for interpreting millimeter wave data, establishing scene signatures, performing mission analyses, and developing system requirements for the design of millimeter wave sensor systems. In this paper, we will present details of the ARMSS code and describe its current use in defining system requirements for the passive millimeter wave camera being developed under the Passive Millimeter Wave Camera Consortium led by TRW.

A passive millimeter-wave camera capable of generating real time displays of the imaged scene, similar to video cameras, has been under development at TRW over the past two years. The camera operates at 89 GHz, has a 15 degree(s) X 10 degree(s) field-of-view, an aperture of 18' diameter, and displays the acquired image at a frame rate of 17 Hz. A major enabling technology is the focal plane array of direct detection MMIC receivers which guarantees reliable and low cost manufacturing of this camera, in addition to providing it with unique operational features. This work reports on progress achieved to date in the development and manufacturing of this new sensor technology.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a target-rich battlefield environment, a shipboard or an airborne radar must maintain situational awareness while tracking and identifying targets. Often the opportunity to dwell on each target long enough for confident identification via high resolution SAR/ISAR imaging will not exist, especially for those engagement geometries where the relative translational motion of the aircraft does not result in large rotation rates. Inadvertent aircraft tactical dither often generates enough target rotational during a brief imaging interval to allow the formation of an ISAR image with low crossrange resolution. We have developed an automated identification procedure that utilizes this resolution, along with high range resolution, to produce confident target identification. The advanced signal processing algorithms employed extract feature measurements from the complex ISAR image. including accurate measurements of the two-dimensional positions, amplitudes and range extents of the dominant target scatterers. A deformable template matching procedure is used to correlate these 'measured features' with those predicted for each candidate aircraft in a database generated from readily available diagrams, photographs and CAD models. After obtaining the optimal fit between the measured and predicted features for each candidate aircraft, the 'most likely' candidate is selected using a conventional Bayes classifier.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In a continuing effort to develop new sensor technologies for the detection of land mines and other UXO, a variety of plastic and metal mines were acquired for detection tests utilizing a passive millimeter wave sensor at 44 GHz and at 12 GHz. These inert mines were surface- laid, covered with dry leaves, or buried in sand or soil, and the resulting target scene was scanned from an overhead position using the single channel sensor, generating a 2D image of the minefield.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Passive millimeter wave (PMMW) sensors have been proposed as forward vision sensors for enhanced vision systems used in low visibility aircraft landing. This work reports on progress achieved to date in the development and manufacturing of a demonstration PMMW camera. The unit is designed to be ground and flight tested starting 1996. The camera displays on a head-up or head-down display unit a real time true image of the forward scene. With appropriate head-up symbology and accurate navigation guidance provided by global positioning satellite receivers on-board the aircraft, pilots can autonomously (without ground assist) execute category 3 low visibility take-offs and landings on non-equipped runways. We shall discuss utility of fielding these systems to airlines and other users.

Passive millimeter wave (PMMW) imaging sensor technology has made significant advances in recent years to permit the development of manufacturable cameras which can be economically produced. In addition to its operation in adverse weather, the PMMW camera is non-emitting which makes it suitable for both military and civilian applications. For example, aircraft executing autonomous landing using GPS, need an all weather, real time, true image of the forward scene during the touch-down, roll-out, turn-off and taxi maneuvers. The PMMW camera not only provides such an image, but is easily implementable as a sensor for the pilot, and as a system which operates in an airport environment. We shall address these issues and discuss other applications of this new sensor technology.

The detection of land mines and other ordnance on the battlefield has grown in importance with their increased use, not only for military personnel, but for civilians after hostilities have ceased. The need for new approaches and sensors to increase the speed and efficiency of methods to clear mines is an issue that must be addressed. A method to detect metal mines, on top of or buried under dry sand, is demonstrated using the passive detection of naturally occurring millimeter wave radiation (at 44 GHz) emanating from the scene. Measurements will be shown that indicate the feasibility of detection of metal under at least 3 inches of dry sand.

The TRW High Power Modular Components (HPMC) program is developing the technology for a high average current ( I avg = 100 mA) superconducting linac for FEL applications. To test the concepts a high brightness injector system is under construction. The injector incorporates a CW 500 kV high voltage electron gun and a pre-accelerator to raise the energy to 1 MeV where the beam may be finally bunched with minimal emittance growth in the face of the large space charge in the bunch. The injector gun cathode is grid modulated to produce beam pulses with 2 A peak current, 500 ps flat-top at 100 MHz repetition rate. The gun was modeled using both steady state (E-GUN) and time dependent (MASK) codes. The modelling using the MASK code showed that because the space charge in the beam is not in equilibrium with the gun focussing elements during the rise and fall of the pulse large emittance growth can occur. We have therefore designed for the rise and fall periods to be as short as possible with a flat-top peak current. We have constructed a test stand to simulate the first stage of the gun, which operates at 100 kV. On the test stand we have demonstrated 500 ps wide flat-topped beam pulses with rise and fall times of approximately 300 ps. The pulser is capable of repetition rates of up to 100 MHz. Measurements have begun of the beam emittance, which has been yielding values for normalized emittance, thus far, of approximately 15π mm mrad. Work is underway to further characterize the gun.

An improved space-time kinetics method that can be applied to the analysis of either fast or thermal reactor transients is presented. The method blends the concepts of formal reduction (i.e., the quasi-static method) and time synthesis into a single unified approach (called quasi-static synthesis) to handle spacetime equations. Preliminary results obtained with the method indicate reduced computer time, while maintaining computational accuracy, when compared to several other kinetics methods presently in use.