Richard L. Wiggins

Real-world noise in hyperspectral imaging systems

It is well known that non-uniform illumination of a spectrometer changes the measured spectra. Laboratory calibration of hyperspectral imaging systems is careful to minimize this effect by providing repeatable, uniform illumination. In hyperspectral measurements the real world images result in non-uniform illumination. We define the resulting variation as real-world noise and we compare real-world noise to other noise sources. Both in-flight performance and calibration transfer between instruments degrade significantly because of real-world noise.

Compact visible to extended-SWIR hyperspectral sensor for unmanned aircraft systems (UAS)

A miniaturized, lightweight turn-key hyperspectral sensor package incorporating a single, monolithic spectrograph, telescope and navigation system is being built for airborne applications on small, Unmanned Aircraft Systems (UAS). The sensor is based on Corning’s existing MicroHSI 410 Vis/NIR Selectable Hyperspectral Airborne Remote sensing Kit (SHARK) currently used for airborne agricultural monitoring. Under DOE sponsorship, we are extending the approach to cover the full spectral range from 0.4-2.5 microns with a single spectrograph. This will enable rapid aerial surveys of vegetative mass, quality, and carbon sequestration. Other applications include mineralogy, agriculture, and intelligence/surveillance/reconnaissance (ISR). The sensor features an Offner-type spectrograph machined from a single transmissive block. The monolithic construction provides an unprecedented combination of high performance, low cost and low size, weight, and power. It has an f/1.4 aperture, 5 nm resolution, and measures only 46mm x 60mm x 76mm. The spectrograph block is coupled to a sterling-cooled, back-thinned, HgCdTe FPA covering 0.4-2.5 micron spectral range. The flight package, including spectrograph, camera, telescope, and navigation system weighs less than 2.4kg and can fit on group 1 UASs. In this paper, we present the design and optical performance of the sensor, and a detailed physical model of detection performance in standard, airborne hyperspectral sensing applications. At 100 Hz data rate, the sensor will achieve shotnoise limited performance with SNR > 250 from 0.4-1.7 microns and SNR<100 between 2-2.3 microns. Operating procedures for airborne monitoring of vegetative properties are also discussed. Initial test flights on a UAS are scheduled for next summer.

The selectable hyperspectral airborne remote sensing kit (SHARK) as an enabler for precision agriculture

Hyperspectral imaging (HSI) has been used for over two decades in laboratory research, academic, environmental and defense applications. In more recent time, HSI has started to be adopted for commercial applications in machine vision, conservation, resource exploration, and precision agriculture, to name just a few of the economically viable uses for the technology. Corning Incorporated (Corning) has been developing and manufacturing HSI sensors, sensor systems, and sensor optical engines, as well as HSI sensor components such as gratings and slits for over a decade and a half. This depth of experience and technological breadth has allowed Corning to design and develop unique HSI spectrometers with an unprecedented combination of high performance, low cost and low Size, Weight, and Power (SWaP). These sensors and sensor systems are offered with wavelength coverage ranges from the visible to the Long Wave Infrared (LWIR). The extremely low SWaP of Corning’s HSI sensors and sensor systems enables their deployment using limited payload platforms such as small unmanned aerial vehicles (UAVs). This paper discusses use of the Corning patented monolithic design Offner spectrometer, the microHSI™, to build a highly compact 400-1000 nm HSI sensor in combination with a small Inertial Navigation System (INS) and micro-computer to make a complete turn-key airborne remote sensing payload. This Selectable Hyperspectral Airborne Remote sensing Kit (SHARK) has industry leading SWaP (1.5 lbs) at a disruptively low price due, in large part, to Corning’s ability to manufacture the monolithic spectrometer out of polymers (i.e. plastic) and therefore reduce manufacturing costs considerably. The other factor in lowering costs is Corning’s well established in house manufacturing capability in optical components and sensors that further enable cost-effective fabrication. The competitive SWaP and low cost of the microHSI™ sensor is approaching, and in some cases less than the price point of Multi Spectral Imaging (MSI) sensors. Specific designs of the Corning microHSI™ SHARK visNIR turn-key system are presented along with salient performance characteristics. Initial focus market areas include precision agriculture and historic and recent microHSI™ SHARK prototype test results are presented.

Hyperspectral grating optimization and manufacturing considerations

Hyperspectral imaging systems are finding broader applications in both the commercial and aerospace markets. It is becoming clear that to optimize the performance of these systems, their instrument transfer function needs to be tailored for each application. Vis-SWIR systems in the full 400nm to 2500nm waveband present particular design and manufacturing challenges. A single blazed grating is inadequate for a system operating in the full vis-SWIR wavelength range. In addition, optical materials and broad band coatings present a challenge for non-reflective systems. An understanding of the application and wavelengths of interest, combined with a judicious choice of a focal plane array, can then lead to an optimized system for the specific application. The ability to tailor the grating and manufacture a wide variety of grating profiles and substrate shapes becomes a significant performance enabler. This paper will discuss how the use of optical, coating, and grating design/analysis software, combined with grating manufacturing techniques assure meeting high performance requirements for different applications.

Compact, high performance hyperspectral systems design and applications

Hyperspectral imaging (HSI) is a technology that is rapidly transitioning from laboratory research and field demonstration to real-world deployment for a variety of applications. These applications include precision agriculture, manufacturing process monitoring, mineral and petroleum exploration, environmental management, disaster mitigation, defense intelligence/surveillance/reconnaissance for threat detection and identification, as well as a host of applications within the bio-medical field. Application-specific algorithms are continuously being developed to support the world-wide expanding use of HSI.

Integrated approach to optomechanical system development

Over the past few decades of computer aided engineering growth there has been much more progress in increasing the power and capability of function specific engineering tools (e.g., optical design, finite element analysis, etc.) than in the integration of and communication between these tools. With only a few notable exceptions, such as FEA being imbedded into solid modeling, the communication method between the function specific tools continues to be dominated by translation to neutral data formats (e.g., IGES, STEP) and file transfer. There are a number of problems with this approach. The translation is a serial process where an engineer has to stop at some point in the design, make the neutral file, send that file to the next function, and wait for feedback. The translation through a neutral format is typically one way so the whole translation process has to be repeated when changes are required. Revision tracking of multiple files for each design iteration is both critical and a likely source of errors. Also, as with any translation, some information is always lost or corrupted in the process. This paper describes some progress that has been made in more tightly integrating optical design, mechanical design, fabrication, and testing of optical systems. Tools have been developed that connect CODE V®[1] to SolidWorks®[2] (bidirectional), compensation of diamond turning CNC from interferometric data, slope analysis from interferometer and profilometer data, and other tools for wavefront error compensation, and electronic nulls. Design, machining, testing and inspection efficiency gains are achieved through tools that consume mechanical solid models in their native format.