Luc Mercier

A real-time high-resolution optical SAR processor

An optical SAR processor prototype exhibiting real-time and fine sampling capabilities has been successfully developed and tested. Synthetic Aperture Radar (SAR) images are typically processed digitally applying dedicated Fast Fourier Transform (FFT) algorithms. These operations are time consuming and require a large amount of processing power and are often performed in one dimension at a time. A true two dimensional Fourier transform may be instead performed through optics, as optical processing provides inherent parallel computing capabilities. By processing the azimuth and slant range directions simultaneously, a reduction in processing time and power is achieved. In addition, the configuration of the optics is such that high resolution images may be obtained at no additional processing cost. The optical SAR processor is also designed to adapt to SAR system parameter changes. It has the capability to produce full Envisat / ASAR scenes from the various image mode swaths (IS1 - IS7) within tens of seconds. This paper reviews the design of the real-time high resolution optical SAR processor prototype and discusses the results of images reconstructed from simulated point targets as well as from Envisat / ASAR data sets.

Full scene SAR processing in seconds using a reconfigurable optronic processor

This paper introduces a compact real-time reconfigurable optronic SAR processor. SAR images are typically processed electronically applying dedicated Fourier transformations. The optronic processor performs these tasks at the speed of light. The prototype has the capability to generate a SAR image blocks in about 1.5 seconds and a complete ASAR scene in about 10 seconds. It may be instantaneously reconfigured to process data from any of the 7 ASAR image swath modes. In addition to being real-time and reconfigurable, the prototype is also light weight, small and low power consuming, thus well-suited for on-board SAR image processing.

Introducing a 384x288 pixel terahertz camera core

Terahertz is a field in expansion with the emergence of various security needs such as parcel inspection and through-camouflage vision. Terahertz wavebands are characterized by long wavelengths compared to the traditional infrared and visible spectra. However, it has recently been demonstrated that a 52 μm pixel pitch microscanned down to an efficient sampling pitch of 26 μm could provide useful information even using a 118.83 μm wavelength. With this in mind, INO has developed a terahertz camera core based on a 384x288 pixel 35 μm pixel pitch uncooled bolometric terahertz detector. The camera core provides full 16-bit output video rate.

A global review of optronic synthetic aperture radar/ladar processing

Synthetic aperture (SA) techniques are currently employed in a variety of imaging modalities, such as radar (SAR) and ladar (SAL). The advantage of fine resolution provided by these systems far outweighs the disadvantage of having large amounts of raw data to process to obtain the final image. Digital processors have been the mainstay for synthetic aperture processing since the 1980’s; however, the original method was optical that is, it employed lenses and other optical elements. This paper provides a global review of a compact light weight optronic processor that combines optical and digital techniques for ultra-fast generation of synthetic aperture images. The overall design of the optronic processor is detailed, including the optical design and data control and handling. As well, its real-time capabilities are demonstrated. Example ENVISAT/ASAR images generated optronically are also presented and compared with ENVISAT Level 1 products. As well, the extended capabilities of optronic processing, including wavefront correction and interferometry are discussed. Finally, a tabletop synthetic aperture ladar system is introduced and SAL images generated using the exact optronic processor designed for SAR image generation are presented.

Catadioptric optics for high-resolution terahertz imager

INO has developed infrared camera systems with microscanning capabilities in order to increase image resolution. It has been shown in previous works that the image quality may be improved even if the pixel pitch is smaller than the point spread function. This paper introduces a catadioptric optics system with fully integrated microscan for improved resolution in the THz band. The design, inspired by the INOs HRXCAM infrared camera core and adapted for terahertz wavelengths, includes two mirrors and one refractive element. It has a 11.9 degree full field of view and an effective F-number of 1.07 over a wide spectral range, from 100 μm to 1.5 mm wavelength. This diffraction limited optics is used to provide video rate high quality THz images. A THz camera, with 160 x 120 pixel and 52 μm pitch detector, is combined with the microscan objective to provide a 320 x 240 pixel image with a 26 μm sampling step. Preliminary imaging results using a THz illumination source at 118 μm wavelength are presented. A comparison between standard and microscanned images is also presented.

Flexible 640 x 480 pixel infrared camera module for fast prototyping

In various military, space and civilian infrared-based applications, there is an important need for fast prototyping. At the very heart, stands a requirement for flexible camera modules that provides a multitude of output formats as well as fast adaptability. Based on this concept, INO has developed an advanced compact camera module that can provide both raw data output as well as fully processed images under a variety of formats such as NTSC, PAL, VGA and GigE. This tool can be used to perform a rapid demonstration of an application concept. The IRXCam-640 camera core is a very flexible module that is based on a 640 x 480 pixels uncooled FPA but which may be rapidly modified to accommodate for other resolutions and sensor types. Providing 16-bit raw signal and 8-bit final image outputs at 60 Hz, the electronics gives total access to the detector configuration parameters. The output is available in NTSC, PAL, and GigE. An additional VGA output can be used as input for a microdisplay. TECless operation minimizes module size and power consumption. If required for absolute measurements, a TEC integrated to the detector package can be controlled with external electronics. The camera core can be configured for outdoors operation from -30°C to +60°C with 200°C scene dynamic range at maximum sensitivity. Windowing capability provides flexibility of frame frequency and operating field of view. The camera can be further coupled with a microscan mechanism to provide a high resolution 1280 x 960 pixel image. In this paper, the camera module is reviewed as well as its performances.

Ultra-rapid optronic processor for instantaneous ENVISAT/ASAR scene observation

This paper introduces a real-time compact optronic SAR processor that has the capability to generate ENVISAT/ASAR image swaths of 100 km × 100 km in 10 seconds exhibiting slant plane sampling distances of 4 meters in azimuth and 1 meter in range. It may be instantaneously reconfigured to process data from any of the 7 ASAR image swath modes. In this respect, numerous SAR image sets may be produced immediately on-demand without bottleneck. A rapid SAR processor that also provides fine ground sampling distances in both azimuth and range directions could provide benefits for such applications as ship detection, landslide and flood monitoring, snow and ice coverage and glacier monitoring.

1280 x 960 pixel microscanned infrared imaging module

The needs of surveillance/detection operations in the infrared range, for industrial, spatial and military applications continuously tend toward larger field of view and resolution while maintaining the system as compact as possible. To answer this need, INO has developed a 1280x960 pixel thermal imager, said HRXCAM, with 22.6° field of view. This system consists in the assembly of a catadioptric optics with microscan mechanism and a detection electronic module based on a 640x480 25μm pitch pixel bolometric detector. The detection module, said IRXCAM, is a flexible platform developed for fast prototyping of varied systems thanks to its ability to support a large range of infrared detectors. With its multiple hardware and software functionalities, IRXCAM can also be used as the complete electronic module of a finalized system. HRXCAM is an example of fast prototyping with IRXCAM and an optical lens that fully demonstrates the imaging performance of the final system. HRXCAM provides 1280x960 pixel images at a nominal 5-15 Hz frequency with 60 mK NETD. It can also be used in the 640x480 mode at 58 Hz with the same sensitivity. In this paper, the catadioptric optics with integrated microscan and IRXCAM architecture and specifications are reviewed. Some typical examples of image obtained with HRXCAM in outdoor conditions are presented.

Real-time optical processor prototype for remote SAR applications

A Compact Real-Time Optical SAR Processor has been successfully developed and tested. SAR, or Synthetic Aperture Radar, is a powerful tool providing enhanced day and night imaging capabilities. SAR systems typically generate large amounts of information generally in the form of complex data that are difficult to compress. Specifically, for planetary missions and unmanned aerial vehicle (UAV) systems with limited communication data rates this is a clear disadvantage. SAR images are typically processed electronically applying dedicated Fourier transformations. This, however, can also be performed optically in real-time. Indeed, the first SAR images have been optically processed. The optical processor architecture provides inherent parallel computing capabilities that can be used advantageously for the SAR data processing. Onboard SAR image generation would provide local access to processed information paving the way for real-time decision-making. This could eventually benefit navigation strategy and instrument orientation decisions. Moreover, for interplanetary missions, onboard analysis of images could provide important feature identification clues and could help select the appropriate images to be transmitted to Earth, consequently helping bandwidth management. This could ultimately reduce the data throughput requirements and related transmission bandwidth. This paper reviews the design of a compact optical SAR processor prototype that would reduce power, weight, and size requirements and reviews the analysis of SAR image generation using the table-top optical processor. Various SAR processor parameters such as processing capabilities, image quality (point target analysis), weight and size are reviewed. Results of image generation from simulated point targets as well as real satellite-acquired raw data are presented.

Towards very high-resolution infrared camera core

In various military, space and civilian infrared applications, there is an important need for fast prototyping. For example, detectors with small pitch compared to the diffraction limited spot radius are now available and their specificities must be studied to optimize the design of the next imaging systems. At the very heart stands a requirement for flexible camera modules that provide a multitude of output formats as well as fast adaptability. Based on this concept, INO has developed an advanced compact camera module IRXCAM that can provide both raw data as well as fully processed images under a variety of outputs: NTSC, DVI, VGA, GigE and Camera Link. This tool can be used to perform a rapid demonstration of concept for a specific application. IRXCAM now supports the bolometric detectors INO IRM160A (160 x 120 52 μm pitch pixels, LWIR and THz), Ulis 04 17 1 (640 x 480 25 μpitch pixels, LWIR) and Ulis 05 25 1 (1024 x 768 17 μm pitch pixels). Reduction of the pixel pitch is a way to improve the compromise between the spatial resolution and the dimensions of an imaging system, mainly by reducing the required optical focal length with constant numerical aperture. Microscanning is another way that provides excellent results in terms of spatial resolution for pixel pitches as small as 25 μm in the LWIR range for F/1 optics. Microscanning also preserves the field of view without increasing the number of pixels of the detector. Finally, microscanning is an efficient way to reduce the aliasing effect of a non unity filling factor, a parameter that becomes increasingly important for small pixels. This paper presents the IRXCAM-1024 camera module, its performances, and its use for microscanning with 17 μm pitch pixels and commercial F/1 and F/0.86 refractive optical lenses.