Linh Ngo Phong

NIRST: a satellite-based IR instrument for fire and sea surface temperature measurement

NIRST is a pushbroom scanning infrared radiometer that makes use of 512×2 arrays of resistive microbolometers. This instrument comprises mainly two cameras, one operating in the spectral band of 3.4-4.2 μm (band 1) and the other in the bands of 10.4-11.3 (band 2) and 11.4-12.3 μm (band 3). It is intended for the retrievals of forest fire and sea surface temperatures in the Aquarius / SAC-D mission. In this mission the satellite will be launched into a Sun Synchronous polar orbit with an ascending node at 6 PM. This orbit suits the need of discriminating forest fires from solar reflections. NIRST is designed to achieve a spatial resolution of 350 m and a swath width of 180 km at nadir. Its field of view can be steered across track up to 500 km on each side to shorten the revisit time. To measure fire intensity temperatures NIRST will perform multispectral scans of ground area in bands 1 and 2 and the acquired data will be analyzed using a double band algorithm. The microbolometer detectors have been designed to exhibit useful dynamic range for this application. It is projected that the detector response in band 1 saturates only when NIRST scans a 350 m ground pixel of average temperature of 700 K. The use of the data acquired in bands 2 and 3 allows for the retrieval of sea surface temperature by means of the split algorithm technique.

Advanced microbolometer detectors for a next-generation uncooled FPA for space-based thermal remote sensing

INO has established a VOx-based uncooled microbolometer detector technology and an expertise in the development of custom detectors and focal plane arrays. Thanks to their low power consumption and broadband sensitivity, uncooled microbolometer detectors are finding an increased number of applications in the field of space-based thermal remote sensing. A mission requirement study has identified at least seven applications with a need for data in the MWIR (3-8 μm), LWIR (8-15 μm) and or FIR (15-100 μm) wavelength bands. The requirement study points to the need for two main classes of uncooled thermal detectors, the first requiring small and fast detectors for MWIR and LWIR imaging with small ground sampling distance, and the second requiring larger detectors with sensitivity out to the FIR. In this paper, the simulation, design, microfabrication and radiometric testing of detectors for these two classes of requirements will be presented. The performance of the experimental detectors closely approach the mission requirements and show the potential of microbolometer technology to fulfill the requirements of future space based thermal imaging missions.

Performances of the SAC-D NIRST flight model radiometer

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration of the United States of America and the Comisión Nacional de Actividades Espaciales of Argentina. Jointly developed by CONAE and the Canadian Space Agency, the New IR Sensor Technology (NIRST) instrument will monitor high temperature events. NIRST has one band in the mid-wave infrared and two bands in the thermal infrared. The baseline design of the NIRST is based on microbolometer technology developed jointly by INO and the CSA. This paper will first present an overview of the design of the NIRST camera module. The manufacturing and qualification activities for the Flight Model will be described and key performance parameters, as measured during the verification campaign, will be reported.

Design, manufacturing, and qualification of an uncooled microbolometer focal plane array–based radiometric package for space applications

Uncooled microbolometer detectors are well suited for space applications due to their low power consumption while still exhibiting adequate performance. Furthermore, the spectral range of their response could be tuned from the mid- to the far-infrared to meet different mission requirements. If radiometric measurements are required, the radiometric error induced by variation of the temperature of the detector environment must be minimized. In a radiometric package, the detector environment is thermally stabilized by means of a temperature-controlled radiation shield. The radiation shield must be designed to prevent stray radiation from reaching the detector. A radiometric packaging technology for uncooled microbolometer FPAs is presented. The selection of materials is discussed and the final choices presented based on thermal simulations and experimental data. The radiometric stability with respect to stray light and variation of the temperature of the environment as well as the different noise components studied by means of the Allan variance are presented. It is also shown that the device successfully passed the prescribed environmental tests without degradation of performance.

Advanced MEMS and Integrated-Optic Components for Multifunctional Integrated Optical Micromachines

Optical technologies can play a strategic role in improving the performance, functionality, and reducing the mass of various spacecraft technologies, such as true time-delay T/R modules for phased-array antennas and optical sensor systems for satellite navigation and systems status. However, current photonic and fiber-optic systems tend to be bulky relative to the requirements for space applications. Micro integrated-optic circuits increase the integration of optical components on a single substrate, to provide multi-function optical processing and switching similar to electronic integrated circuits. This minimizes the number of external optical interconnections required and sensitivity to external vibrations; maximizing the system information capacity, optical throughput, and reliability, while minimizing the overall system size and weight. This paper considers a systematic development of MEMS integrated-optic circuits on SOI for various space application. A unique blend of MEMS, smart-material and photonic technologies is employed to miniaturize the size of the basic components, while improving on the attainable performance.

Far infrared microbolometers for radiometric measurements of ice cloud

Focal planes of 80x60 VOx microbolometers with pixel pitch of 104 μm were developed in support of the remote sensing of ice clouds in the spectral range from 7.9 to 50 μm. A new design that relies on the use of central posts to support the microbolometer platform was shown effective in minimizing the structural deformation usually occurred in platforms of large area. A process for goldblack coating and patterning of the focal plane arrays was established. It was found that the goldblack absorbs more than 98 % and 92 % of incident light respectively at wavelengths shorter and longer than 20 μm. Moreover, a spectral uniformity of better than 96 % was achieved in all spectral channels required for the measurements. The noise figures derived from the data acquired over short periods of acquisition time showed the evidence of a correlation with the format of the addressed sub-arrays. This correlation was not observed in the data acquired over long periods of time, suggesting the presence of low frequency effects. Regardless of the length of acquisition time, an improvement of noise level could be confirmed when the operating temperature was increased. The dependence of responsivity on sub-array format and operating temperature was investigated. The noise equivalent power derived from this study was found to be in the range from 45 to 80 pW, showing that the far infrared focal plane arrays are suited for use in the intended application.

Spaceborne linear arrays of 512×3 microbolometers

Details on the first linear arrays of 512×3 VOx microbolometers operating in space are reported. Arrays of this format are suited for remote sensing where relative motion between the spacecraft and target provides an inherent scanning mechanism. To take full advantage of the linear format, the array is built on a custom readout electronics that enables simultaneous integration of all pixels for scanning periods of up to 140 ms. The output signal from each pixel is digitized to 14 bits using a voltage-to-frequency conversion mechanism. Two arrays, integrated into two spectrally distinct radiometric packages, provide for coregistration of infrared images in three bands centered at 3.8, 10.85, and 11.85 μm for the retrieval of fire and sea surface temperatures. Analysis of the downlinked data confirms the reliable in-orbit operation and consistency with pre-launch characteristics for both arrays. Algorithms have been developed to perform post processing and absolute radiometric calibration of images in all bands. Image deconvolution using Wiener filtering was found effective in recovering the signal loss incurred in the active pixels when observing high temperature events. The in-flight gain and offset values were evaluated for all pixels by means of deep space measurements and cross calibration with reference spaceborne sensors. Preliminary assessment of the images calibrated using these values showed that they are in agreement with those retrieved from GOES sensor.

Earth Observation Using Japanese/Canadian Formation Flying Nanosatellites

Japan Canada Joint Collaboration Satellites (JC2Sat) is a joint project between the Canadian Space Agency (CSA) and the Japan Aerospace Exploration Agency (JAXA). The main objective of the project is to design, build, launch and operate two 18 kg nearly identical nanosatellites that will be launched as a stack and separated in space to demonstrate the feasibility of Autonomous Formation Flight (AFF) based on aerodynamic differential drag only. The specific configuration of the JC2Sat nanosatellites serves as an ideal technology demonstration platform for the Miniature far Infra-Red Radiometer (Mirad) instrument developed jointly by CSA and Institut National d’Optique (INO). Each nanosatellite carries a Mirad instrument for the purpose of Earth’s limb sounding. Based on un-cooled far infrared micro-bolometers, these low mass and low power payloads will co-register the limb profiles in the emission bands of greenhouse gases CO2 and H2O, respectively centered at wavelengths of 15 and 25 μm. The development of JC2Sat is carried out by a united small team consisting of engineers and researchers from both CSA and JAXA. JC2Sat is planned to be ready for launch in 2011. Mission duration is defined to be one year. At the time of writing, the project is in phase C.

Design of the SAC-D/NIRST camera module

Aquarius/SAC-D is a cooperative international mission conducted jointly by the National Aeronautics and Space Administration (NASA) of the United States of America (USA) and the Comisión Nacional de Actividades Espaciales (CONAE) of Argentina. The overall mission targets the understanding of the total Earth system and the consequences of the natural and man-made changes in the environment of the planet. Jointly developed by CONAE and the Canadian Space Agency (CSA), the New IR Sensor Technology (NIRST) instrument will monitor high temperature events on the ground related to fires and volcanic events, and will measure their physical parameters. Furthermore, NIRST will take measurements of sea surface temperatures mainly off the coast of South America as well as other targeted opportunities. NIRST has one band in the mid-wave infrared centered at 3.8 um with a bandwidth of 0.8 um, and two bands in the thermal infrared, centered respectively at 10.85 and 11.85 um with a bandwidth of 0.9 um. The temperature range is from 300 to 600 K with an NEDT < 0.5 K for the mid-infrared band and from 200 to 400 K with an NEDT < 0.4 K for the thermal bands. The baseline design of the NIRST is based on micro-bolometer technology developed jointly by INO and the CSA. Two arrays of 512x3 uncooled bolometric sensors will be used to measure brightness temperatures. The instantaneous field-of-view is 534 microradians corresponding to a ground sampling distance of 350 m at the subsatellite point. A pointing mirror allows a total swath of +/− 500 km. This paper describes the detailed design of the NIRST camera module. Key performance parameters are also presented.

Linear microbolometer arrays for space and terrestrial imaging

Linear detector array formats are suitable for applications where relative motion between the detector and scene provides an intrinsic scanning mechanism, such as industrial inspection systems and satellite-based earth and planetary observation. The linear array format facilitates the introduction readout features not available in 2-D formats and when combined with low cost packaging approaches reduces sensor cost. We present two linear uncooled detector arrays based on VOx microbolometer technology and integrated CMOS readout electronics. The IRL256B is a linear array of 256 detectors on a 52 μm pitch. It includes a parallel array of 256 reference detectors to provide coarse offset correction and substrate temperature drift compensation. The IRL512A consists of 3 parallel lines of 512 pixels on a 39 μm pitch. It is particularly well suited to multi-spectral pushbroom imaging applications. Each pixel includes active and reference detectors to reduce pixel offset, eliminate common mode power supply noise and increase immunity to chip temperature drift. All pixels are integrated in parallel and the data are output in 14-bit digital format on three parallel output buses. The microbolometer detector design can be customized for selected wavelength ranges from NIR to VLWIR. The IRL256B has been integrated in industrial thermal line-scan imagers and spectrometers and may also be employed in uncooled airborne imaging and scanned surveillance or inspection systems. The IRL512A has been selected as the baseline detector for a number of future earth observation satellite missions.