We report on the calibration of the Compact Midwave Imaging Sensor (CMIS) which has been developed by The Johns Hopkins University - Applied Physics Lab (JHU/APL) under a grant from the NASA Earth Science Technology Office (ESTO). At the heart of the CMIS instrument is a newly-developed high operating temperature (HOT) detector made from III-V compounds in a Type II Superlattice design. The instrument is sensitive to 3 particular bands in the IR spectrum which have been noted for their usefulness in determining cloud coverage and temperatures. The bands used were centered at 2.25 μm, 3.75 μm and 4.05 μm. The focal plane array (FPA) was based on the FLIR ISC0405 640×512 pixel readout integrated circuit with 15 μm square pixels. The CMIS design included a 5 zone “butcher block” filter placed in close proximity to the FPA and refractive optical elements contained inside the barrel of the cold shield such that the optics were cooled to approximately the same temperature as the FPA. A small-size, low-power closed-cycle cooler was used to maintain the FPA and the optics at a temperature of 150 K, at which the dark current was low enough to allow integration times longer than 50 ms for cold background scenes. JHU/APL developed the camera control electronics (CCE) and data processing unit (DPU) for running the FPA, performing image processing functions on the data and storing it in memory. The CCE and DPU were designed for possible use on an orbital payload but for the airborne flight the commercial versions of some of the parts specified for spaceflight were used. This paper will describe the laboratory calibration procedures and results.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is developing a compact, light-weight, and lowpower midwave-infrared (MWIR) imager called the Compact Midwave Imaging Sensor (CMIS), under the support of the NASA Earth Science Technology Office Instrument Incubator Program. The goal of this CMIS instrument development and demonstration project is to increase the technical readiness of CMIS, a multi-spectral sensor capable of retrieving 3D winds and cloud heights 24/7, for a space mission. The CMIS instrument employs an advanced MWIR detector that requires less cooling than traditional technologies and thus permits a compact, low-power design, which enables accommodation on small spacecraft such as CubeSats. CMIS provides the critical midwave component of a multi-spectral sensor suite that includes a high-resolution Day-Night Band and a longwave infrared (LWIR) imager to provide global cloud characterization and theater weather imagery. In this presentation, an overview of the CMIS project, including the high-level sensor design, the concept of operations, and measurement capability will be presented. System performance for a variety of different scenes generated by a cloud resolving model (CRM) will also be discussed.
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has created a unique design for a compact, lightweight, and low-power instrument called the Compact Midwave Imaging Sensor (CMIS). Funded by the NASA ESTO Instrument Incubator Program (IIP), the goal of this CMIS development project is to increase the technical readiness of CMIS for retrieval of cloud heights and atmospheric motion vectors using stereo-photometric methods. The low-cost, low size, weight and power (SWaP) CMIS solution will include high operating temperature (HOT) MWIR detectors and a very low power cooler to enable spaceflight in a 6U CubeSat. This paper will provide an overview of the CMIS project to include the high-level sensor design.
The Advanced Computational Sensors Team at the Johns Hopkins University Applied Physics Laboratory and the Johns Hopkins University Department of Electrical and Computer Engineering has been developing advanced readout integrated circuit (ROIC) technology for more than 10 years with a particular focus on the key challenges of dynamic range, sampling rate, system interface and bandwidth, and detector materials or band dependencies. Because the pixel array offers parallel sampling by default, the team successfully demonstrated that adding smarts in the pixel and the chip can increase performance significantly. Each pixel becomes a smart sensor and can operate independently in collecting, processing, and sharing data. In addition, building on the digital circuit revolution, the effective well size can be increased by orders of magnitude within the same pixel pitch over analog designs. This research has yielded an innovative class of a system-on-chip concept: the Flexible Readout and Integration Sensor (FRIS) architecture. All key parameters are programmable and/or can be adjusted dynamically, and this architecture can potentially be sensor and application agnostic. This paper reports on the testing and evaluation of one prototype that can support either detector polarity and includes sample results with visible, short-wavelength infrared (SWIR), and long-wavelength infrared (LWIR) imaging.
Passive millimeter-wave (mmW) sensors are especially suited to persistent surveillance applications due to their ability to operate during day/night conditions and through transient atmospheric obscurants such as clouds, rain and fog. The contrast of targets will change throughout a diurnal heating cycle and this change will be polarization dependent. Simulations are presented from a ray tracing program developed for the mmW regime that has been modified to account for polarization information. Results are shown demonstrating periods during the day when the contrast of certain targets drop to zero for a linear polarization state while the orthogonal state still maintains a high contrast.
A technique is described for displaying polarization information from passive millimeter-wave (mmW) sensors. This technique uses the hue of an image to display the polarization information and the lightness of an image to provide the unpolarized information. The fusion of both images is done in such a way that minimal information is lost from the unpolarized image while adding polarization information within a single image. The technique is applied to experimental imagery collected in a desert environment with two orthogonal linear polarization states of light and the results are discussed. Several objects such as footprints, ground textures, tire tracks, and shrubs display strong polarization features that are clearly visible with this technique, while materials with low polarization signatures such as metal are also clearly visible in the same image.
A passive millimeter-wave sensor based on optical up-conversion that is sensitive to the polarization state of incident
radiation is described. This system up-converts incident millimeter-wave radiation to an optical frequency and then
recreates the polarization state of the millimeter-wave radiation in the optical signal. A division of time approach is then
used to extract the Stokes information from the signal using optical techniques. Results are shown which verify the
feasibility of this approach and demonstrate the ability to control the phase of the signal to enable the measurement of
Stokes information.
As millimeter-wave imaging technology becomes more mature, several applications are emerging for which this
technology may be useful. However, effectively predicting the nuances of millimeter-wave phenomenology on the
usefulness for a given application remains a challenge. To this end, an accurate millimeter-wave scene simulator would
have tremendous value in predicting imager requirements for a given application. Herein, we present a passive
millimeter-wave scene simulator built on the open-source 3d modeling software Blender. We describe the changes made
to the Blender rendering engine to make it suitable for this purpose, including physically accurate reflections at each
material interface, volumetric absorption and scattering, and tracking of both s and p polarizations. In addition, we have
incorporated a mmW material database and world model that emulates the effects of cold sky profiles for varying
weather conditions and frequencies of operation. The images produced by this model have been validated against
calibrated experimental imagery captured by a passive scanning millimeter-wave imager for maritime, desert, and
standoff detection applications.
A new technique for improvised explosive device (IED) creation uses an explosive device buried in foam and covered in
a layer of dirt. These devices are difficult to detect visually, however, their material characteristics make them detectable
by passive millimeter-wave (pmmW) sensors. Results are presented from a test using a mock IED and an outdoor set-up
consisting of two mock IEDs on a dirt background. The results show that the mock IEDs produces a millimeter-wave
signature which is distinguishable from the background surrounding the mock IEDs. Simulations based on the measured
data are presented and a design for a future vehicle mounted sensor is shown.
The polarization properties of radiation can contain additional information beyond what is available with only
an intensity measurement. A full-Stokes polarimeter is capable of measuring the four Stokes parameters which
completely characterizes the polarization of detected radiation. A division of time full-Stokes polarimeter often uses a
rotating polarizing element to measure all four Stokes parameters and this rotation can introduce artifacts due to
wobbling. In this paper a system is proposed which uses an electrically controlled phase bias instead of a rotating
element to create a full-Stokes polarimeter for a millimeter-wave system which utilizes optical up-conversion.
The low attenuation of millimeter-wave radiation propagating through sandstorms has created an interest in using
millimeter-wave imagers in desert environments. The ground in desert environments can have significant differences in
polarization properties depending on the angle of observation. Perturbations to the natural desert surface will change
these polarization properties and by using a polarization difference technique these changes are highlighted. This
technique has been applied to millimeter-wave images from a desert environment for several different objects including
holes in the ground, footsteps, and changes to the surface created by digging.
KEYWORDS: Imaging systems, Calibration, Sensors, Temperature metrology, Data modeling, Visualization, Antennas, Polarization, Absorption, Data acquisition
The unique ability of the millimeter-wave portion of the spectrum to penetrate typical visual obscurants has resulted in a
wide range of possible applications for imagers in this spectrum. Of particular interest to the military community are
imagers that can operate effectively in Degraded Visual Environments (DVE's) experienced by helicopter pilots when
landing in dry, dusty environments, otherwise known as "brownout." One of the first steps to developing operational
requirements for imagers in this spectrum is to develop a quantitative understanding of the phenomenology that governs
imaging in these environments. While preliminary studies have been done in this area, quantitative, calibrated
measurements of typical targets and degradation of target contrasts due to brownout conditions are not available. To
this end, we will present results from calibrated, empirical measurements of typical targets of interest to helicopter pilots
made in a representative desert environment. In addition, real-time measurements of target contrast reduction due to
brownout conditions generated by helicopter downwash will be shown. These data were acquired using a W-band,
dual-polarization radiometric scanner using optical-upconversion detectors.
Passive millimeter-wave (mmW) imaging has many specific defense, security and safety applications, due to the fact
that all terrestrial bodies above absolute zero are emissive, and these wavelengths are not scattered by normal obscurants
such as haze, fog, smoke, dust, sandstorms, clouds, or fabrics. We have previously demonstrated results from the
construction of a 94 GHz passive mmW far-field imaging system utilizing optical upconversion, which imaged in only
horizontal polarization. The effective radiometric temperature of an object is a combination of the object's surface and
scattered radiometric temperatures. The surface radiometric temperature is a function of the object's emissivity, which
is polarization dependent. Imaging with radiometric temperature data from both polarizations will allow a greater
identification of the scene being imaged, and allow the recognition of subtle features which were not previously
observable. This additional functionality is accomplished through the installation of added equipment and programming
on our system, thus allowing the simultaneous data collection of imagery in both polarizations. Herein, we present our
experimental procedures, results and passive mmW images obtained by using our far-field imaging system, a brief
discussion of the phenomenology observed through the application of these techniques, as well as the preliminary details
regarding our work on a 3-D passive mmW simulator capable of true physical polarization dependent effective
emissivity and reflectivity rendering, based on the open-source Blender engine.
In this work we discuss the role that nanodiamond abrasives play in magnetorheological finishing. We hypothesize that,
as the nanodiamond MR fluid is introduced to the magnetic field, the micron sized spherical carbonyl iron (CI) particles
are pulled down towards the rotating wheel, leaving a thin layer of nanodiamonds at the surface of the stiffened MR fluid
ribbon. Our experimental results shown here support this hypothesis. We also show that surface roughness values
inside MRF spots show a strong correlation with the near surface mechanical properties of the glass substrates and with
drag force.
We present a material removal rate model for MRF of optical glasses using nanodiamond MR fluid. The new model
incorporates terms for drag force, polishing particle properties, chemical durability and glass composition into an
existing model that contains only terms for the glass mechanical properties. Experimental results for six optical glasses
are given that support this model.
Research is currently being conducted to better understand the role that nanodiamond abrasives play in the removal process of Magnetorheological Finishing (MRF). The following presents removal rate data for a set of six optical glasses that were spotted (not polished out) with four different MR fluids, as well as texturing/smoothing data for phosphate laser glass LHG-8. Three of the fluids contained nanodiamonds with varying friability levels and the fourth fluid was an abrasive-free fluid that was used as a baseline for comparison. The medium friability nanodiamonds were found to be the most efficient in removing material on LHG-8, and the three silicate glasses, FS, BK-7 and FD-60. The high friability nanodiamond fluid was the most efficient for removal with the titanium and fluro- phosphate glasses EFDS-1 and FCD-1. With this nanodiamond the removal rates of all six glasses followed a mechanical figure of merit. The presence of nanodiamonds in the MR fluid greatly affected the surface texture of LHG-8. The abrasive-free MR fluid caused severe pitting that was either reduced or eliminated once the nanodiamonds were added to the fluid.
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