Hyperspectral cameras are capable of obtaining highly useful data for geology, agriculture, urban planning, and many other applications. Several satellite-based hyperspectral cameras are currently operational, providing hyperspectral data to various users. Even large instruments usually have relatively large ground sampling distance (GSD): 10m or larger in 400 to 1000nm range and 30m or larger in 900 to 2500nm range. GSD is even coarser in hyperspectral cameras for microsatellites. Based on the information from PRISMA 2021 Workshop and our customer’s feedback, the most requested feature for satellite-based hyperspectral cameras is significantly improved GSD. Also, there is a strong demand for smaller microsatellite-compatible hyperspectral cameras. Due to lower mission cost, such cameras can provide hyperspectral data to more users. Additionally, microsatellite constellations could provide swath and revisit time that would be impossible for a single large satellite. Creating a hyperspectral camera with acceptable Signal-to-Noise Ratio (SNR) and small GSD, that would be still compatible with a small platform, is a big challenge. Our approach has been to create a hyperspectral camera that would surpass the current limitations of small satellite platforms, and would provide data that, for some specifications, exceed what is available for free from large instruments. Our focus has been on providing significantly improved GSD, small spatial and spectral misregistration, while keeping acceptable spectral sampling and SNR. The instrument development has been funded by the Norwegian Space Agency. One of the proposed instruments has been selected by the Norwegian Space Agency as the primary payload on an upcoming Norwegian In-Orbit Demonstrator satellite.
We report results from numerical simulations of laser beam propagation through atmospheric turbulence. In particular, we study the statistical variations of the fractional beam energy hitting inside an optical aperture placed at several kilometer distance. The simulations are performed for different turbulence conditions and engagement ranges, with and without the use of turbulence mitigation. Turbulence mitigation is simulated with phase conjugation. The energy fluctuations are deduced from time sequence realizations. It is shown that turbulence mitigation leads to an increase of the mean energy inside the aperture and decrease of the fluctuations even in strong turbulence conditions and long distance engagement. As an example, the results are applied to a high energy laser countermeasure system, where we determine the probability that a single laser pulse, or one of the pulses in a sequence, will provide a lethal energy inside the target aperture. Again, turbulence mitigation contributes to increase the performance of the system at long-distance and for strong turbulence conditions in terms of kill probability. We also discuss a specific case where turbulence contributes to increase the pulse energy within the target aperture. The present analysis can be used to evaluate the performance of a variety of systems, such as directed countermeasures, laser communication, and laser weapons.
In some applications of multi- or hyperspectral imaging, it is important to have a compact sensor. The most compact
spectral imaging sensors are based on spectral filtering in the focal plane. For hyperspectral imaging, it has been
proposed to use a "linearly variable" bandpass filter in the focal plane, combined with scanning of the field of view. As
the image of a given object in the scene moves across the field of view, it is observed through parts of the filter with
varying center wavelength, and a complete spectrum can be assembled. However if the radiance received from the object
varies with viewing angle, or with time, then the reconstructed spectrum will be distorted. We describe a camera design
where this hyperspectral functionality is traded for multispectral imaging with better spectral integrity. Spectral
distortion is minimized by using a patterned filter with 6 bands arranged close together, so that a scene object is seen by
each spectral band in rapid succession and with minimal change in viewing angle. The set of 6 bands is repeated 4 times
so that the spectral data can be checked for internal consistency. Still the total extent of the filter in the scan direction is
small. Therefore the remainder of the image sensor can be used for conventional imaging with potential for using motion
tracking and 3D reconstruction to support the spectral imaging function. We show detailed characterization of the point
spread function of the camera, demonstrating the importance of such characterization as a basis for image reconstruction.
A simplified image reconstruction based on feature-based image coregistration is shown to yield reasonable results.
Elimination of spectral artifacts due to scene motion is demonstrated.
The performance of optical systems is degraded by atmospheric turbulence. Over propagation distances that exceed
several kilometers, it is difficult to evaluate its impact because of terrain variability - a factor that should be taken into
account. However, to optimize performance, the turbulence characteristics and its effect on optical wave propagation
along the propagation path should be known. The understanding of turbulence impact is one of the main objectives of the
NATO group SET 165: "Adaptive Optics (AO) for laser beam delivery, passive and active imaging and turbulence
mitigation". In this paper we describe experiments performed by the NATO SET 165 research group, namely, a set of
atmospheric experiments over a 7 km distance, and discuss some preliminary results of data processing. The experiments
were conducted at the University of Dayton Intelligent Optics Laboratory (UD/IOL) in October 2011. It benefited
significantly from the available optical setups and the infrastructure on the UD/IOL site.
Nonlinear optical conversion of high-energy 1.064 μm pulses from a Q-switched Nd:YAG laser to the mid-infrared
is demonstrated. The experimental setup is based on a two-stage master-oscillator/power-amplifier (MOPA)
design with a KTiOPO4 based MOPA in the first stage and a KTiOAsO4/ZnGeP2 based MOPA in the second
stage. The setup can be tuned to provide output at wavelengths within the transparency range of ZnGeP2. We
obtain more than 8 mJ at 8 μm, and up to 33 mJ in the 3-5 μm wavelength region. The measured beam quality
factors are in the range M2 =2-4 for both wavelength regions.
Nonlinear optical conversion of 1.064 μm pulses from a Q-switched Nd:YAG laser to the mid-infrared is demonstrated
experimentally. The setup is based on a two-stage master-oscillator/power-amplifier (MOPA) design
with a KTiOPO4 based MOPA in the first stage and a KTiOAsO4/ZnGeP2 based MOPA in the second stage.
We obtain more than 8 mJ at 8 μm with a beam quality factor M2 ≈ 3.6.
We present an efficient, high-power mid-infrared laser source using a Thulium fiber laser as pump source. The CW fiber laser pumps a Q-switched Ho:YAG laser which in turn pumps a ZnGeP2-based OPO. We have built a semi-ruggedized version of the laser for countermeasure field trials, and using a 15 W fiber laser we obtained 5.2 W output power in the 3-5 μm band. We also present work on scaling up the power by using a 65 W fiber laser as the pump. Simulations and initial experiments suggest that the scaled-up version could produce more than 25 W in the mid-IR.
Nonlinear optical conversion of 500 mJ pulses from a Nd:YAG laser to the mid-infrared is demonstrated in a two-step architecture. Using a type 2 phase matched KTiOPO4-based master-oscillator/power-amplifier (MOPA) architecture for conversion to 2 μm, 140 mJ signal at 2.08 μm with M2 = 2.3 and 80 mJ idler at 2.18 μm were obtained. Using 58 mJ of the signal beam to pump a ZnGeP2-based MOPA, we have obtained 21 mJ in the 3-5 μm range with M2 ≈ 15.
We present a simple design for efficient generation of high average power in the 3-5 μm wavelength range. Using a 15 W thulium-doped fibre laser to pump a Q-switched 2.1 μm Ho:YAG laser, we obtain 9.2 W average output power with excellent beam quality. The 2.1 μm output is used to pump a ZnGeP2-based OPO, resulting in 4.6 W average output power in the 3.6-5.2 μm range with beam quality M2 < 1.4.
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