Wildfires increasingly endanger people and property due to the growing population in the wildland urban interface, drought, and climate change. In the United States in 2023 over 1,000,000 acres burned in the western CONUS with no fire encompassing over 100,000 acres. Also, tragically the Lahaina Fire in Hawaii caused the deaths of over 100 people. In Canada, the extreme 2023 fire season resulted in almost 18,500,000 hectares burned, which was a factor of 2.6 larger than the previous high in 1995. The economic losses are enormous with resource expenditures running into the billions and insured losses running into the tens of billions of dollars in the United States. We propose the application of an imaging spectrometer for pre- and post-fire assessments and fire detection. MIT Lincoln Laboratory has developed three critical technologies that are applicable to the wildfire problem. The first is a compact spectrometer, the Chrisp Compact VNIR/SWIR Imaging Spectrometer (CCVIS), that can be modularly implemented for a wide-field imaging spectrometer. The second is the digital focal plane array (DFPA) technology with different detector materials, such as InGaAs or Mercury Cadmium Telluride (MCT), and extremely large well depths exceeding 108 electrons. The DFPA is critical for this application since traditional FPAs will saturate even for relatively cool fires with small spatial sample fill fractions. The DFPA also has sufficient signal to noise performance for pre- and post-fire products such as canopy cover, fuel quantification, and burnt area quantification and monitoring. The third is the TeraByte InfraRed Delivery (TBIRD) space-to-ground optical link that has a maximum data rate of 800 Gbps, which will not be addressed here. A small satellite implementation in a low Earth orbit (∼450 km) will have an entrance pupil on the order of 10 cm for a 50 m ground sample distance (GSD).
The Chrisp Compact Visible-SWIR Spectrometer (CCVIS) was developed by MIT Lincoln Laboratory as a high performance, low Size-Weight-Power (SWAP) slit-based hyperspectral sensor that provides comparable performance to current fielded units but more than an order smaller in packaging volume. The design takes advantage of a flat, immersed grating and a color-corrected catadioptric layout to provide >25mm slit length operating from 380-2500nm. We show results from our efforts to design and build an environmentally robust variant which undergoing Technology Readiness Level 6 testing for future spaceflight.
The study of aquatic ecosystems is an important research area addressing diverse problems such as carbon sequestration in coastal margins and wetlands, kelp and seagrass studies, coral reefs, harmful algal blooms and hypoxia, and carbon cycling in this dynamic environment. The application of an imaging spectrometer to aquatic ecosystem study is particularly challenging due to low water-leaving radiance levels adjacent to the shore region with its higher values. The Committee on Earth Observation Satellites (CEOS) has established more stringent performance standards for the visible/near infrared wavelengths than are typically available in imaging spectrometer designs. We have recently developed a compact form imaging spectrometer, the Chrisp Compact VNIR/SWIR Imaging Spectrometer (CCVIS), that facilitates their modular usage with a wide field telescope without sacrificing performance. The CCVIS design and the operational concept have predicted performance that approaches the CEOS standards. The envisioned satellite implementation requires a pitchback maneuver where the imaging of the slit projected onto the surface is slowly scanned while recording focal plane array readouts at a higher rate thereby avoiding saturation over the land surface while obtaining a high signal-to-noise ratio over the water. The effective frame rate is determined by the time it takes to scan the projected slit one ground sample distance (GSD). This approach has the added benefit of measuring a range of angles during a single GSD acquisition, providing insight into the bidirectional reflectance distribution function (BRDF).
The Integrated LCRD Low-Earth Orbit User Modem and Amplifier Terminal (ILLUMA-T) payload will be launched to the International Space Station (ISS) in 2023. ILLUMA-T is an optical communications payload that will make the ISS the first space-based user to communicate with NASA’s Laser Communications Relay Demonstration (LCRD). The system will support all-optical forward links up to 150 Mbps and return links up to 1 Gbps. The payload recently underwent system level Thermal VACuum (TVAC) functional testing at MIT Lincoln Laboratory. We present an overview of the payload’s TVAC functional tests and results.
There is an increasing number of applications for rapid deployment mid-wave infrared (MWIR) and long-wave infrared (LWIR) optical systems, especially for proof-of-concept. These systems are typically placed in test environments where they need an environmental enclosure window for protection. Traditional IR windows, like Germanium and Zinc Selenide, often have high costs and long fabrication lead times, especially for custom designs. Thin, readily available polymers have potential of solving this problem where they may have high enough transmission in the IR to be of use as an inexpensive environmental enclosure window. This paper outlines 33 polymer materials that have been tested as candidates for IR windows by measuring transmission and reflection and then calculating values of refractive index and extinction ratio from the measurements. We have identified 7 polymer materials as having high enough transmission to be used as an IR window. Further testing was done to characterize wavefront error and image quality of MWIR and LWIR cameras with these polymer windows. The combined results show 3 promising materials in the MWIR and LWIR.
Free-space laser communication systems are increasingly implemented on state of the art satellites for their high-speed connectivity. This work outlines a demonstration of the Modular, Agile, Scalable Optical Terminal (MAScOT) we have developed to support Low-Earth Orbit (LEO) to deep-space communication links. In LEO, the MAScOT will be implemented on the International Space Station to support the Integrated Laser Communications Relay Demonstration (LCRD) LEO User Modem and Amplifier Terminal (ILLUMA-T) program. ILLUMA-T's overarching objective is to demonstrate high bandwidth data transfer between LEO and a ground station via a geosynchronous (GEO) relay satellite. Outside of LEO, the MAScOT will be implemented on the Artemis-II mission to demonstrate high data rate optical communications to and from the moon as part of the Optical to Orion (O2O) program. Both missions leverage the same modular architecture despite varying structural, thermal, and optical requirements. To achieve sufficient performance, the terminal relies on a nested tracking loop to realize sub-arcsecond pointing across a ±120 ° elevation and ±175° azimuth field of regard.
Using a novel computational imaging architecture, we double the field of view of a long-wave infrared microbolometer camera while maintaining resolution. Due to the compact designs enabled by this architecture and the critical impact of resolution on classification performance, this approach is compelling for surveillance applications where low size, weight, power and cost (SWaP-C) systems are desired. We detail the optical design, characterization, and performance of a compact, refractive, optically multiplexed imaging system for use in the long-wave infrared (8-12 μm). A pair of prisms are used to divide the aperture and expose the uncooled microbolometer focal plane to two fields of view simultaneously, doubling the number of output pixels and the horizontal field of view. The image is reconstructed by rotating the prisms about the optical axis, inducing opposing vertical shifts in the two channels. Focal length, field of view, MTF, and NEDT are used to compare performance to a conventional camera. Shifting methods for proper demultiplexing are discussed, and reconstructed images are offered as a demonstration of system performance.
A computed tomographic imaging spectrometer (CTIS) disperses the three-dimensional (3-D) datacube (x, y, λ) into two-dimensional (2-D) projections on a focal plane array (FPA). The 3-D datacube is subsequently reconstructed from these 2-D projections using iterative computed tomography algorithms. Conventional designs achieve the 3-D to 2-D mapping by incorporating an optimized disperser. However, these dispersers suffer from the linearity constraint inherent in the first-order grating equation. This constraint means that many of the FPA's pixels are either unilluminated or they are used to image redundant projections; in both cases, they can not be used to increase the datacube's spectral resolution. Here, we outline various hardware improvements that increase the CTIS's spectral resolution by making use of these previously unilluminated or redundant pixels. Specifically, we incorporated a new disperser based on a 2-D grating prism and a division of aperture approach. Included is an optical design analysis of the system, in addition to an experimental characterization of the instrument's performance. Lastly, the new disperser is compared to a conventional disperser to quantify the increased spectral resolution.
A computed tomographic imaging spectrometer (CTIS) is an instrument which can simultaneously obtain image spatial
and spectral information without moving parts in a single focal plane array integration time. When this instrument is
combined with a channeled spectropolarimeter, the instrument can also obtain complete Stokes polarization information
at each resolution element. The combined instrument, called a computed tomographic imaging channeled
spectropolarimeter (CTICS), has been developed in the visible wavelength region. This paper summarizes the CTICS
design and results obtained from data acquired during field testing of the CTICS instrument.
Two imaging systems have been designed and built to function as snapshot imaging spectropolarimeters; one system
made to operate in the visible part of the spectrum, the other for the long wavelength infrared, 8 to 12 microns. The
devices are based on computed tomographic imaging channeled spectropolarimetry (CTICS), a unique technology that
allows both the spectra and the polarization state for all of the wavelength bands in the spectra to be simultaneously
recorded from every spatial position in an image with a single integration period of the imaging system. The devices
contain no moving parts and require no scanning, allowing them to acquire data without the artifacts normally associated
with scanning spectropolarimeters. Details of the two imaging systems will be presented.
A computed tomography imaging channeled spectropolarimeter (CTICS) is a combination of a computed tomography
imaging spectrometer (CTIS) and a channeled spectropolarimeter (CHSP). The CTICS instrument can simultaneously
obtain image spatial and spectral information as well as polarization Stokes vectors at each resolution element in a single
focal plane array (FPA) integration time with no moving parts. An instrument has been designed and built for the
visible wavelength region at the University of Arizona. Performance testing is underway. In this work, we present
initial results from data acquired during testing of the CTICS instrument.
A Computed Tomography Imaging Spectrometer (CTIS) is an imaging spectrometer which can acquire a multi-spectral
data set in a single snapshot (one focal plane array integration time) with no moving parts. Currently, CTIS instruments
use a specially designed computer generated hologram (CGH) to disperse the light from a given spectral band into a
grid of diffraction orders. The capabilities of the CTIS instrument can be greatly improved by replacing the static CGH
dispersing element with a reconfigurable liquid crystal spatial light modulator. The liquid crystal spatial light modulator
is tuned electronically, enabling the CTIS to remain a non-scanning imaging spectrometer with no moving parts. The
ability to rapidly reconfigure the dispersing element of the CTIS allows the spectral and spatial resolution to change by
varying the number of diffraction orders, diffraction efficiency, etc. In this work, we present the initial results of using
a fully addressable, 2-D liquid crystal spatial light modulator as the dispersing element in a CTIS instrument.
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