Far infrared microbolometers for radiometric measurements of ice cloud

Phong, Linh Ngo; Proulx, Christian; Oulachgar, Hassane; Châteauneuf, François

doi:10.1117/12.2076219

Cited by 4 publications

(5 citation statements)

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“…As a result, the NER ranges from approximately 0.01 to 0.02 W m −2 sr −1 depending on spectral band and number of pixels used. To illustrate the resolution of the FIRR in terms of brightness temperature, the NER is converted into noise equivalent temperature difference (NETD, e.g., Niklaus et al, 2008), that is the temperature increase a perfect BB should experience for its radiance change to equal the NER. Figure 6 shows the variations of NETD with BB temperature for a NER of 0.01 W m −2 sr −1 .…”

Section: Instrument Resolutionmentioning

confidence: 99%

A microbolometer-based far infrared radiometer to study thin ice clouds in the Arctic

Libois¹,

Proulx

Ivanescu³

et al. 2016

Atmos. Meas. Tech.

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Abstract. A far infrared radiometer (FIRR) dedicated to measuring radiation emitted by clear and cloudy atmospheres was developed in the framework of the Thin Ice Clouds in Far InfraRed Experiment (TICFIRE) technology demonstration satellite project. The FIRR detector is an array of 80 × 60 uncooled microbolometers coated with gold black to enhance the absorptivity and responsivity. A filter wheel is used to select atmospheric radiation in nine spectral bands ranging from 8 to 50 µm. Calibrated radiances are obtained using two well-calibrated blackbodies. Images are acquired at a frame rate of 120 Hz, and temporally averaged to reduce electronic noise. A complete measurement sequence takes about 120 s. With a field of view of 6°, the FIRR is not intended to be an imager. Hence spatial average is computed over 193 illuminated pixels to increase the signal-to-noise ratio and consequently the detector resolution. This results in an improvement by a factor of 5 compared to individual pixel measurements. Another threefold increase in resolution is obtained using 193 non-illuminated pixels to remove correlated electronic noise, leading an overall resolution of approximately 0.015 W m−2 sr−1. Laboratory measurements performed on well-known targets suggest an absolute accuracy close to 0.02 W m−2 sr−1, which ensures atmospheric radiance is retrieved with an accuracy better than 1 %. Preliminary in situ experiments performed from the ground in winter and in summer on clear and cloudy atmospheres are compared to radiative transfer simulations. They point out the FIRR ability to detect clouds and changes in relative humidity of a few percent in various atmospheric conditions, paving the way for the development of new algorithms dedicated to ice cloud characterization and water vapor retrieval.

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Section: Instrument Resolutionmentioning

confidence: 99%

A microbolometer-based far infrared radiometer to study thin ice clouds in the Arctic

Libois¹,

Proulx

Ivanescu³

et al. 2016

Atmos. Meas. Tech.

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“…The reference configuration of the instrument is 10 bands, and the NER is assumed the same for each channel, equal to 0.01 W m −2 sr −1 . This is consistent with a thermal sensor coated with gold black which has spectrally flat absorbance through the whole IR range [e.g., Ngo Phong et al , ], and with the absence of significant spectral differences in the transmittance along the optical path. Such characteristics are expected for a grating‐based or filter wheel‐based radiometer.…”

Section: Motivation and Methodsmentioning

confidence: 99%

“…The development of FIR spectrometers has been hindered for several reasons: (1) radiometric responsivity of existing sensors is much less in the FIR than in the MIR; (2) observations from the ground are in most locations useless since the atmosphere is essentially opaque in the FIR; (3) hyperspectral instruments in the MIR, such as AIRS or Infrared Atmospheric Sounding Interferometer (IASI) [ Blumstein et al , ], already contain much information about the atmosphere. There has been in the last decade a renewed interest for satellite missions in the FIR, though, mainly fostered by the availability of new technologies based on uncooled thermal sensors such as thermopiles [ McCleese et al , ], pyroelectrics [ Palchetti et al , ], and microbolometers [ Ngo Phong et al , ]. Such sensors, when coated with gold black, have sufficient sensitivities and are easier to deploy in space than cooled systems.…”

Section: Introductionmentioning

confidence: 99%

Added value of far‐infrared radiometry for remote sensing of ice clouds

Libois

Blanchet

2017

JGR Atmospheres

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Several cloud retrieval algorithms based on satellite observations in the infrared have been developed in the last decades. However, these observations only cover the midinfrared (MIR, λ < 15 μm) part of the spectrum, and none are available in the far‐infrared (FIR, λ≥ 15 μm). Using the optimal estimation method, we show that adding a few FIR channels to existing spaceborne radiometers would significantly improve their ability to retrieve ice cloud radiative properties. For clouds encountered in the polar regions and the upper troposphere, where the atmosphere is sufficiently transparent in the FIR, using FIR channels would reduce by more than 50% the uncertainties on retrieved values of optical thickness, effective particle diameter, and cloud top altitude. Notably, this would extend the range of applicability of current retrieval methods to the polar regions and to clouds with large optical thickness, where MIR algorithms perform poorly. The high performance of solar reflection‐based algorithms would thus be reached in nighttime conditions. Since the sensitivity of ice cloud thermal emission to effective particle diameter is approximately 5 times larger in the FIR than in the MIR, using FIR observations is a promising venue for studying ice cloud microphysics and precipitation processes. This is highly relevant for cirrus clouds and convective towers. This is also essential to study precipitation in the driest regions of the atmosphere, where strong feedbacks are at play between clouds and water vapor. The deployment in the near future of a FIR spaceborne radiometer is technologically feasible and should be strongly supported.

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“…In this sense it is very similar to the Mars Climate Sounder (McCleese et al, 2007) and the Diviner Lunar Radiometer Experiment (Paige et al, 2010), which use uncooled thermal sensors to probe radiation in the FIR. The FIRR sensor is a 2-D array of uncooled microbolometers coated with gold black (Ngo Phong et al, 2015), and radiometric calibration is achieved with two reference blackbodies (BB) at distinct temperatures. The latter consist of cavities whose temperature and emissivity are well known, so that the radiance they emit is accurately estimated.…”

Section: The Far-infrared Radiometermentioning

confidence: 99%

Airborne observations of far-infrared upwelling radiance in the Arctic

Libois¹,

Ivanescu

Blanchet³

et al. 2016

Atmos. Chem. Phys.

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Abstract. The first airborne measurements of the FarInfraRed Radiometer (FIRR) were performed in April 2015 during the panarctic NETCARE campaign. Vertical profiles of spectral upwelling radiance in the range 8-50 µm were measured in clear and cloudy conditions from the surface up to 6 km. The clear sky profiles highlight the strong dependence of radiative fluxes to the temperature inversion typical of the Arctic. Measurements acquired for total column water vapour from 1.5 to 10.5 mm also underline the sensitivity of the far-infrared greenhouse effect to specific humidity. The cloudy cases show that optically thin ice clouds increase the cooling rate of the atmosphere, making them important pieces of the Arctic energy balance. One such cloud exhibited a very complex spatial structure, characterized by large horizontal heterogeneities at the kilometre scale. This emphasizes the difficulty of obtaining representative cloud observations with airborne measurements but also points out how challenging it is to model polar clouds radiative effects. These radiance measurements were successfully compared to simulations, suggesting that state-of-the-art radiative transfer models are suited to study the cold and dry Arctic atmosphere. Although FIRR in situ performances compare well to its laboratory performances, complementary simulations show that upgrading the FIRR radiometric resolution would greatly increase its sensitivity to atmospheric and cloud properties. Improved instrument temperature stability in flight and expected technological progress should help meet this objective. The campaign overall highlights the potential for airborne far-infrared radiometry and constitutes a relevant reference for future similar studies dedicated to the Arctic and for the development of spaceborne instruments.

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Far infrared microbolometers for radiometric measurements of ice cloud

Cited by 4 publications

References 5 publications

A microbolometer-based far infrared radiometer to study thin ice clouds in the Arctic

A microbolometer-based far infrared radiometer to study thin ice clouds in the Arctic

Added value of far‐infrared radiometry for remote sensing of ice clouds

Airborne observations of far-infrared upwelling radiance in the Arctic

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