Radiometric Measurements Research Articles

Simulation of a simultaneous traceable spectroradiometric calibration of an imaging spectrometer

Spectroradiometric calibration aims to determine the instrumental spectral response function (ISRF) parameters and radiometric coefficients of an instrument’s spectral bands across all spatial pixels. Typically, this is done by making separate spectral and radiometric calibration measurements. We present a method for the simultaneous traceable spectroradiometric calibration of an imaging spectrometer, using the Spectroscopically Tunable Absolute Radiometric, calibration and characterisation, Optical Ground Support Equipment (STAR-cc-OGSE) facility. We performed the forward simulation of calibration data acquisition by convolving input spectra with the sensor model’s response and simulated a slit scattering function (SSF)-based calibration, allowing for both ISRF coefficients and the absolute spectral responsivities to be accurately retrieved from a single series of measurements. We show how the SSF method minimizes uncertainties compared to the traditional spectroradiometric calibration approach.

Statystical Analysis in Integration of Thermal Imaging and GNSS Satellite Measurements in Relation to Geological Structure as a Method to Improve the Accuracy of Displacement Determination of Engineering Structures

Numerous publications have confirmed the important contribution of applying GNSS satellite measurements in geologically unstable areas to the displacement measurements of engineering objects. Along with linking GNSS measurements of benchmarks considered to be stable in the long term to the nearest reference stations at appropriate measurement intervals. So, it was possible to improve the accuracy of measurements of vertical and horizontal coordinates in the area of Szczecin, ushering in coordinate errors of less than 2 and 5 mm. For objects of strategic use such as natural gas tanks located in salt formations, however, these values are too high. The displacement of salt formations is 0.5 mm per year. Therefore, I decided to review existing measurement methods in two areas with different geological structures - Szczecin and Wroclaw NW and SW Poland - as numerous spectrums of SAR methods. As a different method, I present the advantages of the radiometric method with the prospect of performing surveys in the abovementioned areas. The publication focuses on statistical analyses, and GNSS and radiometric field measurements are in progress.

Analysis of Radio Science Data from the KaT Instrument of the 3GM Experiment During JUICE’s Early Cruise Phase

The JUpiter Icy Moon Explorer (JUICE) mission, launched on 14 April 2023, aims to explore Jupiter and its Galilean moons, with arrival in the Jovian system planned for mid-2031. One of the scientific investigations is the Geodesy and Geophysics of Jupiter and the Galilean Moons (3GM) radio science experiment, designed to study the interior structures of Europa, Callisto, and Ganymede and the atmospheres of Jupiter and the Galilean moons. The 3GM experiment employs a Ka-band Transponder (KaT) to enable two-way coherent range and Doppler measurements used for the gravity experiment and an Ultra Stable Oscillator (USO) for one-way downlink occultation experiments. This paper analyzes KaT data collected at the ESA/ESTRACK ground station in Malargüe, Argentina, during the Near-Earth Commissioning Phase (NECP) in May 2023 and the first in-cruise payload checkout (PC01) in January 2024. The radiometric data were fitted using both NASA’s Mission Analysis, Operations, and Navigation Toolkit Environment (MONTE) and ESA’s General Orbit Determination and Optimization Toolkit (GODOT) software. The comparison of the orbital solutions showed an excellent agreement. In addition, the Doppler and range residuals allowed a preliminary assessment of the quality of the radiometric measurements. During the NECP pass, the radio link data showed a range-rate noise of 0.012 mm/s at 1000 s integration time, while the root mean square of the range residuals sampled at 1 s was 8.4 mm. During the first payload checkout, the signal power at the KaT input closely matched the value expected at Jupiter, due to a specific ground station setup. This provided early indications of the 3GM’s performance during the Jovian phase. In this test, the accuracy of range data at an integration time of 1s, particularly sensitive to the link signal-to-noise ratio, degraded to 13.6 cm, whilst the range-rate accuracy turned out to be better than 0.003 mm/s at 1000 s, thanks to the accurate tropospheric delay calibration system (TDCS) available at the Malargue station (inactive during NECP).

Калибровка внутренних эталонов шумового сигнала радиометра по внешним источникам Igor A.

The possibility of using solid-state noise signal sources as internal standards in a two-stop modulation radiometer is discussed. The dependence of the accuracy of radiometric measurements on the temperatures of internal noise standards is estimated. The possibility of calibrating internal solid-state noise sources against external reference objects with known noise temperatures is being investigated. Formulas for calculating the noise temperatures of internal standards based on known temperatures of external standards are given. The prospect of using a new method of calibration of internal standards to improve the accuracy and stability of radiometric sensing of soils for remote determination of moisture content and soil surface temperature as an element of a precision farming system is analyzed.

In-mission synergy of science and navigation ephemeris products—Potential benefits for JUICE statistical Delta-V expenditure and beyond

In 2031 the JUICE spacecraft will perform a multi-flyby tour of the Jovian system. Next to the radiometric tracking that is performed for navigation operations, the dedicated radio science instrument (3GM) collects high-accuracy radiometric measurements during the flybys.We investigate the capability of the radio science data to provide improved moon state knowledge during navigational operations. We introduce ephemeris updates from radio science data into our simulated navigation operations and examine the potential savings of statistical ΔV for corrective manoeuvres. A navigation orbit determination (OD) solution was simulated for the multi-flyby tour of JUICE, including the resulting state knowledge evolution of the Galilean moons. The OD was extended by an interface for external moon ephemeris updates, which was used to evaluate the impact of radio science generated external ephemerides on the statistical ΔV budgets for post-flyby cleanup manoeuvres.The moon state knowledge evolution during navigation operation showed a rapid reduction of the a-priori moon state uncertainty, for which the navigational tracking data coverage of the long, early tour arcs was identified as the driving factor. As a result of the longer tracking arcs, the moon state knowledge from navigation data results improves more quickly during the initial phase of the tour. Since the impact of moon state knowledge on the corrective manoeuvres is largest in this initial phase, the comparative analysis of the statistical ΔV cost shows that the adoption of radio science ephemeris products does not effectuate significant ΔV savings. Instead we showed that in order to achieve substantial ΔV savings improvements of Europa’s and Ganymede’s ephemerides are required ahead of JUICE’s arrival.While the analysis concludes that data synergies are unlikely to benefit the navigational operations, it highlights other potential synergies between the navigation and radio science data. A comparatively strong signature of Io’s dynamics was found in the simulated navigation data along the long early tour arcs, which could be leveraged for the benefit of the new global moon ephemeris solutions after JUICE.

A Prospective Study Comparing the Use of Radiometric Measurements in CBCT and DEXA Scans of the Spine to Measure Bone Mineral Density in Postmenopausal Women

ABSTRACT Introduction: This study evaluated BMD using radiomorphometric indices from conebeam computed tomography (CBCT) scans of the mandible, comparing them with dualenergy Xray absorptiometry (DEXA) scans of the spine. Results: The study emphasizes the robustness of DEXAderived T scores for assessing bone health and guiding treatment in postmenopausal women.

On the closure relationship among shortwave radiometric measurements under a cold climate during winter

To support the Baseline Surface Radiation Network initiative, a new radiometric station was set up in Qiqihar, China, which has a monsoon-influenced hot-summer humid continental climate (Dwa) under the Köppen–Geiger climate classification, which is extremely rare in the world. Through a two-month operation in winter, it was observed that the station suffered from some nonclosure problems that impacted the quality of its measurements—the summation of the beam and diffuse components do not agree well with the global one. This work therefore investigates the possible causes of the problems and presents a set of quality checks to identify the causes. It is found that the problems originate from the mis-leveling of the sun tracker and frost deposition on the pyrheliometer, and once they are fixed, the closure relationship is maintained.

Rain detection for rain-contaminated ground-based microwave radiometer data using physics-informed machine learning method

Because the radiation signal is strongly influenced by emission and scattering from rain, microwave radiometer data suffer from rain contamination. The traditional method of using rain gauges to detect rain for microwave radiometers has limitations. For example, it can only detect rain that reaches the ground and is ineffective for raindrops suspended in the atmosphere that can still contaminate remote sensing data. This article presents a rain detection method for microwave radiometer measurements, based on Gradient Boosted Decision Trees (GBDT). First, the characteristic that the increase in microwave radiometer brightness temperature when raindrops are present in the atmosphere, along with the seasonal dependency of rainfall patterns, is combined with meteorological variables to form feature vectors. Then, the GBDT is employed to classify data into rain-free and rain-contaminated categories. Microwave radiometer (MWR) measurements and simultaneous Micro Rain Radar (MRR) target classification collected from the Swiss Plateau in 2008 are utilized to train the model, which is subsequently tested using two testing schemes: ten-fold cross-validation technique and time series test sets. Compared with the detection accuracy of the integrated liquid water (ILW) threshold method (73.6% and 68.3%) in both testing schemes, our GBDT-based method achieved superior accuracy, recording approximately 100% and 98.4%, respectively. The proposed method exhibits strong generalization capabilities, allowing it to directly detect rain contamination in time series data and effectively overcome the time dependence of rainfall occurrence. In addition, compared with the ILW threshold method, the GBDT-based method considers various rainfall patterns contained in various seasons. Features selected for this method enable its direct application to other tropospheric microwave radiometer systems.

Improving solution availability and temporal consistency of an optimal-estimation physical retrieval for ground-based thermodynamic boundary layer profiling

Abstract. Thermodynamic profiles in the atmospheric boundary layer can be retrieved from ground-based passive remote sensing instruments like infrared spectrometers and microwave radiometers with optimal-estimation physical retrievals. With a high temporal resolution on the order of minutes, these thermodynamic profiles are a powerful tool to study the evolution of the boundary layer and to evaluate numerical models. In this study, we describe three recent modifications to the Tropospheric Remotely Observed Profiling via Optimal Estimation (TROPoe) retrieval framework, which improve the availability of valid solutions for different atmospheric conditions and increase the temporal consistency of the retrieved profiles. We present methods to enhance the availability of valid solutions retrieved from infrared spectrometers by preventing overfitting and by adding information from an additional spectral band in high-moisture environments. We show that the characterization of the uncertainty of the input and the choice of spectral infrared bands are crucial for retrieval performance. Since each profile is retrieved independently from the previous one, the time series of the thermodynamic variables contain random uncorrelated noise, which may hinder the study of diurnal cycles and temporal tendencies. By including a previous retrieved profile as input to the retrieval, we increase the temporal consistency between subsequent profiles without suppressing real mesoscale atmospheric variability. We demonstrate that these modifications work well at midlatitudes, polar and tropical sites, and for retrievals based on infrared spectrometer and microwave radiometer measurements.

Investigating the occurrence and predictability of pitch angle scattering events at ADITYA-Upgrade tokamak with the electron cyclotron emission radiometer

This paper describes the experimental analysis and preliminary investigation of the predictability of pitch angle scattering (PAS) events through the electron cyclotron emission (ECE) radiometer signals at the ADITYA-Upgrade (ADITYA-U) tokamak. For low-density discharges at ADITYA-U, a sudden abnormal rise is observed in the ECE signature while other plasma parameters are unchanged. Investigations are done to understand this abrupt rise that is expected to occur due to PAS. The rise time is as fast as 100 μs with a single step and/or multiple step rise in ECE radiometer measurements. This event is known to limit the on-axis energy of runaway electrons. Being a repetitive event, the conditions of its repetitive occurrence can be investigated, thereby exploring the possibility of it being triggered and surveyed as an alternate runaway electron mitigation plan. Functional parameterization of such events with other discharge parameters is obtained and the possibility to trigger these events is discussed. PREDICT code is used to investigate the possible interpretations for the PAS occurrence through modeling and supporting the ECE observations. The trigger values so obtained experimentally are set as input criteria for PAS occurrence. Preliminary modeling investigations provide reliable consistency with the findings.

Combining low- and high-frequency microwave radiometer measurements from the MOSAiC expedition for enhanced water vapour products

Abstract. In the central Arctic, high-quality water vapour observations are sparse due to the low density of meteorological stations and uncertainties in satellite remote sensing. Different reanalyses also disagree on the amount of water vapour in the central Arctic. The Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition provides comprehensive observations that are suitable for evaluating satellite products and reanalyses. Radiosonde observations provide high-quality water vapour estimates with a high vertical but a low temporal resolution. Observations from the microwave radiometers (MWRs) on board the research vessel Polarstern complement these observations through high temporal resolution. In this study, we demonstrate the high accuracy of the combination of the two MWRs HATPRO (Humidity and Temperature Profiler) and MiRAC-P (Microwave Radiometer for Arctic Clouds – Passive). For this purpose, we developed new retrievals of integrated water vapour (IWV) and profiles of specific humidity and temperature using a neural network approach, including observations from both HATPRO and MiRAC-P to utilize their different water vapour sensitivity. The retrievals were trained with the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5) and synthetic MWR observations simulated with the Passive and Active Microwave radiative TRAnsfer tool (PAMTRA). We applied the retrievals to synthetic and real observations and evaluated them with ERA5 and radiosondes launched during MOSAiC, respectively. To assess the benefit of the combination of HATPRO and MiRAC-P compared to single MWR retrievals, we compared the errors with respect to MOSAiC radiosondes and computed the vertical information content of the specific humidity profiles. The root mean squared error (RMSE) of IWV was reduced by up to 15 %. Specific humidity biases and RMSE were reduced by up to 75 % and 50 %, respectively. The vertical information content of specific humidity could be increased from 1.7 to 2.4 degrees of freedom. We also computed relative humidity from the retrieved temperature and specific humidity profiles and found that RMSE was reduced from 45 % to 15 %. Finally, we show a case study demonstrating the enhanced humidity profiling capabilities compared to the standard HATPRO-based retrievals. The vertical resolution of the retrieved specific humidity profiles is still low compared to radiosondes, but the case study revealed the potential to resolve major humidity inversions. To what degree the MWR combination detects humidity inversions, also compared to satellites and reanalyses, will be part of future work.

Radiation protection and natural building materials in cultural heritage

IntroductionBuildings that constitute cultural heritage and that are the identity of a defined geographical area are increasingly being restored to offer the community historical places to enjoy. Often the restoration preserves the original structure and building materials, which are usually natural stones. In this study, a radioprotection protocol dedicated to this kind of built environment was proposed and validated.MethodsAfter identifying the two predominant types of building material stones (Rosso ammonitico and Pietra Serena), radiometric measurements for natural gamma-emitting radionuclides (Ra-226, Th-232, and K-40) and measurements of the emanation coefficient and calculation of the exhalation rate of radon gas were carried out.ResultsThe two types of stone have a content of natural radionuclides that do not exceed the levels recommended by the regulations. The difference between the two types of stone is of an order of magnitude indicating that the red ammonite has a greater radiological impact than the pietra serena.DiscussionThe results, in addition to ensuring the radioprotection of the population, highlighted the need to increase the number of this kind of investigations to implement scientific knowledge and serve the stakeholders involved.

On sea ice emission modeling for MOSAiC's L-band radiometric measurements

Abstract The retrieval of sea ice thickness using L-band passive remote sensing requires robust models for emission from sea ice. In this work, measurements obtained from surface-based radiometers during the MOSAiC expedition are assessed with the Burke, Wilheit and SMRT radiative transfer models. These models encompass distinct methodologies: radiative transfer with/without wave coherence effects, and with/without scattering. Before running these emission models, the sea ice growth is simulated using the Cumulative Freezing Degree Days (CFDD) model to further compute the evolution of the ice structure during each period. Ice coring profiles done near the instruments are used to obtain the initial state of the computation, along with Digital Thermistor Chain (DTC) data to derive the sea ice temperature during the analyzed periods. The results suggest that the coherent approach used in the Wilheit model results in a better agreement with the horizontal polarization of the in situ measured brightness temperature. The Burke and SMRT incoherent models offer a more robust fit for the vertical component. These models are almost equivalent since the scattering considered in SMRT can be safely neglected at this low frequency, but the Burke model misses an important contribution from the snow layer above sea ice. The results also suggest that a more realistic permittivity falls between the spheres and random needles formulations, with potential for refinement, particularly for L-band applications, through future field measurements.

Realization of (400∼950) nm detector-based spectral radiance scale at NIM

Abstract Detector-based radiometric measurement is advantageous in terms of measurement uncertainty. National Institute of Metrology China (NIM) has developed a facility for detector-based spectral radiance scale realization in the range of (400∼950) nm. The scale is realized based on a tunable-laser coupled integrating sphere source using galvanometer-driven mirror, and a silicon trap reference standard detector calibrated directly against NIM’s primary standard for spectral power responsivity and NIM’s effective area calibration facility for apertrue area. Sources and transfer standards are characterized, and spectral radiance responsivity can be measured with uncertainties at the (0.2∼0.4) % level.

Statistics of precipitable water vapour, optical thickness and cloud cover within the Northern part of Eurasia

One of the most important tasks in astroclimatic studies of possible locations for the Eurasian Submillimeter Telescopes is estimating statistics of precipitable water vapour, optical thickness and cloud cover. In this paper, the statistics of precipitable water vapour and total cloud cover within Northern part of Eurasia are studied using ERA-5 reanalysis. Optical thickness statistics at a wavelength of 3 mm were obtained using the Liebe model from the ERA-5 reanalysis for the region where the BTA is located. The most favorable astroclimatic zones of Eurasia include Tibet and the Eastern Pamirs, certain regions of the Sayan Mountains, Altai and Mts within Dagestan. Also we verified the ERA-5 reanalysis data using radiosonde data, GNSS measurement data and radiometric measurements for 2021.

Do anomalously dense hot Jupiters orbit stealth binary stars?

ABSTRACT The Wide Angle Search for Planets (WASP) survey used transit photometry to discover nearly 200 gas-giant exoplanets and derive their planetary and stellar parameters. Reliable determination of the planetary density depends on accurate measurement of the planet’s radius, obtained from the transit depth and photodynamical determination of the stellar radius. The stellar density and hence the stellar radius are typically determined in a model-independent way from the star’s reflex orbital acceleration and the transit profile. Additional flux coming from the system due to a bright, undetected stellar binary companion can, however, potentially dilute the transit curve and radial velocity signal, leading to underestimation of the planet’s mass and radius, and to overestimation of the planet’s density. In this study, we cross-check the published radii of all the WASP planet-host stars, determined from their transit profiles and radial velocity curves, against radiometric measurements of stellar radii derived from their angular diameters (via the infrared flux method) and trigonometric parallaxes. We identify eight systems showing radiometric stellar radii significantly greater than their published photodynamical values: WASPs 20, 85, 86, 103, 105, 129, 144, and 171. We investigate these systems in more detail to establish plausible ranges of angular and radial velocity separations within which such ‘stealth binaries’ could evade detection, and deduce their likely orbital periods, mass ratios, and flux ratios. After accounting for the dilution of transit depth and radial velocity amplitude, we find that, on average, the planetary densities for the identified stealth binary systems should be reduced by a factor of 1.3.

Intelligent Radiometric Calibration System for Ocean Color Satellite Sensors

Abstract To achieve the integration of multiple ocean color (OC) sensors’ radiometric calibration tasks into a single system, we have developed an intelligent on-orbit radiometric calibration system called the Generalized Radiometric Calibration Entity for Ocean Color (Grace-OC). The system features real-time data downloading capabilities and integrates three calibration methods: onboard calibration, system vicarious calibration and cross calibration, enabling intelligent selection of on-orbit radiometric calibration methods tailored to the calibration sensors. Compared to other calibration systems, we have improved the universality and efficiency of the system by establishing high-spectral aerosols and Rayleigh lookup tables (LUTs) which are verified consistency through a comparative analysis with operational LUTs releasing by National Aeronautics and Space Administration (NASA) in this paper. Building upon this foundation, we have integrated a comprehensive analysis function for calibration coefficients to automatically construct degradation models of the radiometric measurement performance, and to achieve mutual verification between different calibration methods. We applied Grace-OC to HY1C/D and verified the feasibility of the intelligent selection calibration methods and the stability of the calibration system, achieving a calibration accuracy of up to 0.5%. Simultaneously, the precision of degradation models of the radiometric measurement performance is confirmed through Grace-OC, and the on-orbit radiometric calibration task was ultimately completed within 6 minutes for each per scene. Based on the above applications, Grace-OC has demonstrated its universality for various OC sensors, as well as the stability of on-orbit radiometric calibration tasks and the efficiency of operational speed.

Investigation of the Innovative Combined Reuse of Phosphate Mine Waste Rock and Phosphate Washing Sludge to Produce Eco-Friendly Bricks

Phosphate mining generates substantial quantities of waste rock during the extraction of sedimentary ores, leading to significant environmental concerns as these wastes accumulate around mining sites. The industry is under increasing pressure to adopt more sustainable practices, necessitating considerable financial investments in remediation and technological advancements. Addressing these challenges requires a holistic strategy that balances social responsibility, environmental preservation, and economic viability. This study proposes an innovative, cost-effective, and environmentally friendly method to manufacture compressed stabilized earth bricks by combining the valorization of phosphate waste rock (PWR) and phosphate washing sludge (PWS). These bricks offer numerous advantages, including low embodied energy, robust mechanical performance, and excellent insulation and thermal properties. Initially, a Toxicity Characteristic Leaching Procedure (TCLP) test and radiometric surface contamination measurement, carried out on raw materials (PWR and PWS), showed that the results were below the permissible limits. Then, the chemical, mineralogical, and geotechnical properties of the raw materials were characterized. Subsequently, various mixtures were formulated in the laboratory using PWR and PWS, with and without cement as a stabilizer. Optimal formulations were identified and scaled up for pilot production of solid bricks with dimensions of 250 × 125 × 75 mm3. The resulting bricks exhibited thermal conductivity and water absorption coefficients that satisfied standard requirements. This method not only addresses the environmental issues associated with phosphate mining waste but also provides a sustainable solution for building materials production.

Application of Satellite Microwave Radiometric Methods to Analyze the Relationship of Tropical Cyclogenesis with Water Vapor Transport in the Atlantic

Some possibilities of using microwave radiometric measurements from the EOS Aqua and GCOM-W1 satellites to study the influence of tropical waves in the Atlantic on cyclogenesis processes in the Gulf of Mexico by monitoring the spatial and temporal variability of water vapor fields in the Gulf are illustrated. Examples of the use of satellite images of atmospheric humidity fields obtained from DMSP and EOS Aqua satellites are given to demonstrate the processes of transformation of tropical waves into Atlantic hurricanes Bonnie (1998), Frances (2004), Ivan (2004).

Uncertainties in radiometric measurements of the ocean surface from above water and helicopter hyperspectral and polarimetric observations

A new system was assembled with a snapshot hyperspectral imager and a polarimetric camera for quantifying uncertainties in aquatic remote sensing applications. The hyperspectral imager measures radiances from a field-of-view (FOV) creating imagery for each of its spectral bands. The polarimetric camera measures the Stokes vector components of the radiance. A combination of polarimetric and hyperspectral measurements provides data about the wind-roughened surface in various water and sky conditions. Uncertainties in the total radiance L t in unpolarized and polarized modes are estimated by observations from the ships in two ocean cruises, from a nearshore platform, and a helicopter in the Chesapeake Bay showing that uncertainties are a combination of the effects of the reflected sky from the surface (ρL s ), water leaving radiance (L w ), and Rayleigh scattering; the impact of the latter increases with the height.