Accurate radiometric calibration is a key feature of modern infrared cameras. Considering the newly available infrared
focal plane arrays (FPA) exhibiting very high spatial resolution and faster readout speed, we developed a method to
provide a dedicated radiometric calibration of every pixel. The novel approach is based on detected fluxes rather than
detected counts as is customarily done. This approach features many advantages including the explicit management of
the main parameter used to change the gain of the camera, namely the exposure time. The method not only handles the
variation of detector spectral responsivity across the FPA pixels but also provides an efficient way to correct for the
change of signal offset due to camera self-emission and detector dark current. The method is designed to require as few
parameters as possible to enable a real-time implementation for megapixel-FPAs and for data throughputs larger than
100 Mpixels/s. Preliminary results with a high-speed 3 μm to 5 μm infrared camera demonstrate that the method is
viable and yields small radiometric errors.
Advancements in Mercury Cadmium Telluride (MCT) focal plane arrays (FPA) in recent years have allowed high performance longwave infrared imagers to prosper. In particular molecular and gas/chemical spectroscopy applications can be vastly advanced with these new products. However, for the transition from single pixel spectrometers to FPA base imaging spectrometers to succeed, a couple of parallel advancements must be made as well. Most Fourier transform spectrometers currently available are designed specifically for a 1 mm single pixel detector. Scientists who try to convert these systems into imaging spectrometers quickly run into throughput issues when FPAs reach sizes of up to 12.5mm, thus limiting the performance and greatly impacting the detection capabilities. Furthermore, for large FPAs the readout time can be significantly longer than the integration time. In turn, this requires slower sweep speeds with a higher degree of control of the scanning mechanism. The benefit of these new technologies in spectroscopy can only be demonstrated with a system optimally designed for imaging spectroscopy. This paper will address the issues of imaging spectroscopy and will show how an instrument designed for specifically imaging applications can dramatically improve the performance of the system and quality of the data acquired.
Standoff detection, identification and quantification of chemicals require sensitive spectrometers with calibration capabilities. Recent developments in LWIR focal plane arrays combined with the mastering of Fourier-Transform Spectrometer technology allow the realization of an imaging spectrometer specifically designed for chemical imaging. The spectral and radiometric calibration of the instrument enables the processing of the data to detect the chemicals with spectral signatures in the 8-12 μm region. Spectral images are processed and the contrast between different pixels is used to map the chemicals. Telops is building the field-portable instrument. This paper presents the requirements for chemical detection in the LWIR, how the system is broken down into different modules and the details of each of these modules: calibration, interferometer, datacube acquisition and processing, and the main controller. The system has real-time processing capabilities of the measured data. Performance prediction is presented as well.
The development of precision farming requires new tools for plant nutritional stress monitoring. An operational
fluorescence system has been designed for vegetation status mapping and stress detection at plant and field scale. The
instrument gives relative values of fluorescence at different wavelengths induced by the two-excitation sources. Lightinduced
fluorescence has demonstrated successful crop health monitoring and plant nutritional stress detection
The spectral response of the plants has first been measured with an hyperspectral imager using laser-induced
fluorescence. A tabletop imaging fluorometer based on flash lamp technology has also been designed to study the
spatial distribution of fluorescence on plant leaves. For field based non-imaging system, LED technology is used as
light source to induce fluorescence of the plant. The operational fluorescence system is based on ultraviolet and blue
LED to induce fluorescence. Four narrow fluorescence bands centered on 440, 520, 690 and 740nm are detected. The
instrument design includes a modular approach for light source and detector. It can accommodate as many as four
different light sources and six bands of fluorescence detection. As part of the design for field application, the instrument
is compatible with a mobile platform equipped with a GPS and data acquisition system.
The current system developed by Telops/GAAP is configured for potato crops fluorescence measurement but can easily
be adapted for other crops. This new instrument offers an effective and affordable solution for precision farming.