Calibrating ground‐based microwave radiometers: Uncertainty and drifts

Küchler, Nils; Turner, David D.; Löhnert, Ulrich; Crewell, Susanne

doi:10.1002/2015rs005826

Cited by 31 publications

(17 citation statements)

References 29 publications

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“…The radiometer was calibrated by comparing the measured data from subjects with the emission levels from known standard sources [24]. The standard sources were carbon loaded foam absorbers at liquid Nitrogen (77 K) and ambient (293 K) temperature, as illustrated in Figure 2.…”

Section: Calibration and Initial Measurementsmentioning

confidence: 99%

Electromagnetic Signatures of Human Skin in the Millimeter Wave Band 80-100 GHZ

Owda

Salmon

Rezgui

2018

PIER B

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Abstract-Due to changes in global security requirements attention is turning to new means by which anomalies on the human body might be identified. For security screening systems operating in the millimeter wave band anomalies can be identified by measuring the emissivities of subjects. As the interaction of millimeter waves with the human body is only a fraction of a millimeter into the skin and clothing has a small, but known effect, precise measurement of the emission and reflection of this radiation will allow comparisons with the norm for that region of the body and person category. A technique to measure the human skin emissivity in vivo over the frequency band 80 GHz to 100 GHz is developed and described. The mean emissivity values of the skin of a sample of 60 healthy participants (36 males and 24 females) measured using a 90 GHz calibrated radiometer were found to range from 0.17±0.005 to 0.68±0.005. The lower values of emissivity are a result of measuring particularly thin skin on the inner wrist, volar side of the forearm, and back of hand, whereas higher values of emissivity are results of measuring thick skin on the outer wrist, dorsal surface of the forearm, and palm of hand. The mean differences in the emissivity between Asian and European male participants were calculated to be in the range of 0.04 to 0.11 over all measurement locations. Experimental measurements of the emissivity for male and female participants having normal and high body mass index indicate that the mean differences in the emissivity are in the range of 0.05 to 0.15 for all measurement locations. These results show the quantitative variations in the skin emissivity between locations, gender, and individuals. The mean differences in the emissivity values between dry and wet skin on the palm of hand and back of hand regions were found to be 0.143 and 0.066 respectively. These results confirm that radiometry can, as a non-contact method, identify surfaces attached to the human skin in tens of seconds. These results indicate a route to machine anomaly detection that may increase the through-put speed, the detection probabilities and reduce the false alarm rates in security screening portals.

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Section: Calibration and Initial Measurementsmentioning

confidence: 99%

Electromagnetic Signatures of Human Skin in the Millimeter Wave Band 80-100 GHZ

Owda

Salmon

Rezgui

2018

PIER B

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“…The radiometer needs to be well calibrated to exploit the optimal calibration coefficients in order to convert detected intensities into BTs. To that end a liquid nitrogen cooled load considered as a blackbody at the boiling temperature of 77 K is generally used (Küchler et al, 2016). A liquid nitrogen calibration was performed at the beginning of the experimental campaign at the end of November 2014.…”

Section: Hatpro Mwrmentioning

confidence: 99%

Combining ground-based microwave radiometer and the AROME convective scale model through 1DVAR retrievals in complex terrain: an Alpine valley case study

Martinet

Cimini²,

Angelis

et al. 2017

Atmos. Meas. Tech.

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Abstract. A RPG-HATPRO ground-based microwave radiometer (MWR) was operated in a deep Alpine valley during the Passy-2015 field campaign. This experiment aims to investigate how stable boundary layers during wintertime conditions drive the accumulation of pollutants. In order to understand the atmospheric processes in the valley, MWRs continuously provide vertical profiles of temperature and humidity at a high time frequency, providing valuable information to follow the evolution of the boundary layer. A one-dimensional variational (1DVAR) retrieval technique has been implemented during the field campaign to optimally combine an MWR and 1 h forecasts from the French convective scale model AROME. Retrievals were compared to radiosonde data launched at least every 3 h during two intensive observation periods (IOPs). An analysis of the AROME forecast errors during the IOPs has shown a large underestimation of the surface cooling during the strongest stable episode. MWR brightness temperatures were monitored against simulations from the radiative transfer model ARTS2 (Atmospheric Radiative Transfer Simulator) and radiosonde launched during the field campaign. Large errors were observed for most transparent channels (i.e., 51-52 GHz) affected by absorption model and calibration uncertainties while a good agreement was found for opaque channels (i.e., 54-58 GHz). Based on this monitoring, a bias correction of raw brightness temperature measurements was applied before the 1DVAR retrievals. 1DVAR retrievals were found to significantly improve the AROME forecasts up to 3 km but mainly below 1 km and to outperform usual statistical regressions above 1 km. With the present implementation, a root-mean-square error (RMSE) of 1 K through all the atmospheric profile was obtained with values within 0.5 K below 500 m in clear-sky conditions. The use of lower elevation angles (up to 5 • ) in the MWR scanning and the bias correction were found to improve the retrievals below 1000 m. MWR retrievals were found to catch deep near-surface temperature inversions very well. Larger errors were observed in cloudy conditions due to the difficulty of ground-based MWRs to resolve high level inversions that are still challenging. Finally, 1DVAR retrievals were optimized for the analysis of the IOPs by using radiosondes as backgrounds in the 1DVAR algorithm instead of the AROME forecasts. A significant improvement of the retrievals in cloudy conditions and below 1000 m in clear-sky conditions was observed. From this study, we can conclude that MWRs are expected to bring valuable information into numerical weather prediction models up to 3 km in altitude both in clear-sky and cloudy-sky conditions with the maximum improvement found around 500 m. With an accuracy between 0.5 and 1 K in RMSE, our study has also proven that MWRs are capable of resolving deep near-surface temperature inversions observed in complex terrain during highly stable boundary layer conditions.

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“…The HALO Microwave Package (HAMP, Mech et al, 2014) comprises microwave radiometers with 26 channels in the range between 20 and 183 GHz and a 35 GHz cloud radar. The radiometer modules and radar antenna are mounted below the fuselage inside the belly pod (see Fig.…”

Section: Instrument Descriptionmentioning

confidence: 99%

“…The radiometer modules and radar antenna are mounted below the fuselage inside the belly pod (see Fig. 1 of Mech et al, 2014) with a nadir viewing direction. Mech et al (2014) illustrate the sensitivity of the different measurements with respect to hydrometeors.…”

Section: Instrument Descriptionmentioning

confidence: 99%

A unified data set of airborne cloud remote sensing using the HALO Microwave Package (HAMP)

Konow

Jacob

Ament

et al. 2019

Earth Syst. Sci. Data

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Abstract. Cloud properties and their environmental conditions were observed during four aircraft campaigns over the North Atlantic on 37 flights. The Halo Microwave Package (HAMP) was deployed on the German research aircraft HALO (High Altitude Long Range Research Aircraft) during these four campaigns. HAMP comprises microwave radiometers with 26 channels in the frequency range between 20 and 183 GHz and a 35 GHz cloud radar. The four campaigns took place between December 2013 and October 2016 out of Barbados and Iceland. Measured situations cover a wide range of conditions including the dry and wet season over the tropical Atlantic and the cold and warm sectors of midlatitude cyclones. The data set we present here contains measurements of the radar reflectivity factor and linear depolarization ratio from cloud radar, brightness temperatures from microwave radiometers and atmospheric profiles from dropsondes. It represents a unique combination of active and passive microwave remote sensing measurements and 525 in situ-measured dropsonde profiles. The data from these different instruments are quality controlled and unified into one common format for easy combination of data and joint analysis. The data are available from the CERA database for the four campaigns individually (https://doi.org/10.1594/WDCC/HALO_measurements_1, https://doi.org/10.1594/WDCC/HALO_measurements_2, https://doi.org/10.1594/WDCC/HALO_measurements_3, https://doi.org/10.1594/WDCC/HALO_measurements_4). This data set allows for analyses to gain insight into cloud properties and the atmospheric state in remote regions over the tropical and midlatitude Atlantic. In this paper, we describe the four campaigns, the data and the quality control applied to the data.

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Calibrating ground‐based microwave radiometers: Uncertainty and drifts

Cited by 31 publications

References 29 publications

Electromagnetic Signatures of Human Skin in the Millimeter Wave Band 80-100 GHZ

Electromagnetic Signatures of Human Skin in the Millimeter Wave Band 80-100 GHZ

Combining ground-based microwave radiometer and the AROME convective scale model through 1DVAR retrievals in complex terrain: an Alpine valley case study

A unified data set of airborne cloud remote sensing using the HALO Microwave Package (HAMP)

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