Development of a Dynamically Re-Configurable Radio-Frequency Interference Detection System for L-Band Microwave Radiometers.

Real-Time RFI Detection and Flagging (RT-RDF) for microwave radiometers is a versatile new FPGA algorithm designed to detect and flag Radio-Frequency Interference (RFI) in microwave radiometers. This block utilizes computationally-efficient techniques to identify and analyze RF signals, allowing the system to take appropriate measures to mitigate interference and maintain reliable performance. With L-Band microwave radiometry as the main application, this RFI detection algorithm focuses on the Kurtogram and Spectrogram to detect non-Gaussian behavior. To gain further modularity, an FFT-based filter bank is used to divide the receiver's bandwidth into several sub-bands within the band of interest of the instrument, depending on the application. Multiple blanking strategies can then be applied in each band using the provided detection flags. The algorithm can be re-configured in the field, for example with dynamic integration times to support operation in different environments, or configurable thresholds to account for variable RFI environments. A validation and testing campaign has been performed on multiple scenarios with the ARIEL commercial microwave radiometer, and the results confirm the excellent performance of the system.

Semi-automated segmentation methods of SSTR PET for dosimetry prediction in refractory meningioma patients treated by SSTR-targeted peptide receptor radionuclide therapy.

OBJECTIVES: Tumor dosimetry with somatostatin receptor-targeted peptide receptor radionuclide therapy (SSTR-targeted PRRT) by 177Lu-DOTATATE may contribute to improved treatment monitoring of refractory meningioma. Accurate dosimetry requires reliable and reproducible pretherapeutic PET tumor segmentation which is not currently available. This study aims to propose semi-automated segmentation methods to determine metabolic tumor volume with pretherapeutic 68Ga-DOTATOC PET and evaluate SUVmean-derived values as predictive factors for tumor-absorbed dose. METHODS: Thirty-nine meningioma lesions from twenty patients were analyzed. The ground truth PET and SPECT volumes (VolGT-PET and VolGT-SPECT) were computed from manual segmentations by five experienced nuclear physicians. SUV-related indexes were extracted from VolGT-PET and the semi-automated PET volumes providing the best Dice index with VolGT-PET (Volopt) across several methods: SUV absolute-value (2.3)-threshold, adaptative methods (Jentzen, Otsu, Contrast-based method), advanced gradient-based technique, and multiple relative thresholds (% of tumor SUVmax, hypophysis SUVmean, and meninges SUVpeak) with optimal threshold optimized. Tumor-absorbed doses were obtained from the VolGT-SPECT, corrected for partial volume effect, performed on a 360° whole-body CZT-camera at 24, 96, and 168 h after administration of 177Lu-DOTATATE. RESULTS: Volopt was obtained from 1.7-fold meninges SUVpeak (Dice index 0.85 ± 0.07). SUVmean and total lesion uptake (SUVmeanxlesion volume) showed better correlations with tumor-absorbed doses than SUVmax when determined with the VolGT (respective Pearson correlation coefficients of 0.78, 0.67, and 0.56) or Volopt (0.64, 0.66, and 0.56). CONCLUSION: Accurate definition of pretherapeutic PET volumes is justified since SUVmean-derived values provide the best tumor-absorbed dose predictions in refractory meningioma patients treated by 177Lu-DOTATATE. This study provides a semi-automated segmentation method of pretherapeutic 68Ga-DOTATOC PET volumes to achieve good reproducibility between physicians. CLINICAL RELEVANCE STATEMENT: SUVmean-derived values from pretherapeutic 68Ga-DOTATOC PET are predictive of tumor-absorbed doses in refractory meningiomas treated by 177Lu-DOTATATE, justifying to accurately define pretherapeutic PET volumes. This study provides a semi-automated segmentation of 68Ga-DOTATOC PET images easily applicable in routine. KEY POINTS: • SUVmean-derived values from pretherapeutic 68Ga-DOTATOC PET images provide the best predictive factors of tumor-absorbed doses related to 177Lu-DOTATATE PRRT in refractory meningioma. • A 1.7-fold meninges SUVpeak segmentation method used to determine metabolic tumor volume on pretherapeutic 68Ga-DOTATOC PET images of refractory meningioma treated by 177Lu-DOTATATE is as efficient as the currently routine manual segmentation method and limits inter- and intra-observer variabilities. • This semi-automated method for segmentation of refractory meningioma is easily applicable to routine practice and transferrable across PET centers.

Objective monitoring of laser tattoo removal in human volunteers using an innovative optical technique: A proof of principle.

OBJECTIVES: Assess the suitability of the technique for objective monitoring of laser tattoo removal by an extended treatment protocol. MATERIALS AND METHODS: One half of the tattoo in the first volunteer was treated with nanosecond and the other half with picosecond laser pulses at 1064 nm. In the second subject, four test areas were treated repeatedly using different radiant exposures from 1.5 to 6 J/cm2 . Measurements of diffuse reflectance spectra and photothermal radiometric transients were performed 4-20 weeks after each treatment session. Inverse Monte Carlo analysis based on a three-layer model of tattooed skin was applied to assess the tattoo characteristics and analyze their changes. RESULTS: The results clearly indicate a gradual reduction of the ink content and an increase of the subsurface depth of the tattoo layer with all treatments at a radiant exposure of 3 J/cm2 or higher. The observed dependences on laser pulse duration, radiant exposure, and a number of treatments are in excellent agreement with visual fading of the tattoo. CONCLUSIONS: The presented methodology enables noninvasive characterization of tattoos in human skin and objective monitoring of the laser removal treatment.

The Microwave Temperature and Humidity Profiler: Description and Preliminary Results.

This manuscript presents the Microwave Temperature and Humidity Profiler (MTHP), a dual-band spectroradiometer designed for measuring multi-incidence angle temperature and humidity atmospheric profiles from an aircraft platform. The MTHP bands are at 60 GHz for measuring the oxygen complex lines, therefore at this band, MTHP has a hyperspectral radiometer able to provide 2048 channels over an 8 GHz bandwidth, and 183 GHz for measuring water vapor, which only uses four channels since this absorption band's spectral richness is simpler. The MTHP builds upon the Microwave Temperature Profiler (MTP) with the inclusion of the hyperspectral radiometer. The instrument's design, components, and calibration methods are discussed in detail, with a focus on the three-point calibration scheme involving internal calibration loads and static air temperature readings. Preliminary results from the Technological Innovation into Iodine and GV aircraft Environmental Research (TI3GER) campaign are presented, showcasing the instrument's performance during flights across diverse geographical regions. The manuscript presents successful antenna temperature measurements at 60 GHz and 183 GHz. The hyperspectral measurements are compared with a simulated antenna temperature using the Atmospheric Radiative Transfer Simulator (ARTS) showing an agreement better than R2 > 0.88 for three of the flights analyzed. Additionally, the manuscript draws attention to potential Radio Frequency Interference (RFI) effects observed during a specific flight, underscoring the instrument's sensitivity to external interference. This is the first-ever airborne demonstration of a broadband and hyperspectral multi-incidence angle 60 GHz measurement. Future work on the MTHP could result in an improved spatial resolution of the atmospheric temperature vertical profile and, hence, help in estimating the Planetary Boundary Layer (PBL) with better accuracy. The MTHP and its hyperspectral multi-incidence angle at 60 GHz have the potential to be a valuable tool for investigating the PBL's role in atmospheric dynamics, offering insights into its impact on Earth's energy, water, and carbon cycles.

Recent Progress in Modulated Photothermal Radiometry.

In this review, the emerging work using a technique known as modulated photothermal radiometry (MPTR) is evaluated. As MPTR has matured, the previous discussions on theory and modeling have become increasingly limited in their applicability to the current state of the art. After a brief history of the technique, the currently used thermodynamic theory is explained, highlighting the commonly applied simplifications. The validity of the simplifications is explored via modeling. Various experimental designs are compared, and the differences are explored. New applications, as well as emerging analysis techniques, are presented to emphasize the trajectory of MPTR.

Pulsed Photothermal Radiometric Depth Profiling of Bruises by 532 nm and 1064 nm Lasers.

Optical techniques are often inadequate in estimating bruise age since they are not sensitive to the depth of chromophores at the location of the bruise. To address this shortcoming, we used pulsed photothermal radiometry (PPTR) for depth profiling of bruises with two wavelengths, 532 nm (KTP laser) and 1064 nm (Nd:YAG laser). Six volunteers with eight bruises of exactly known and documented times of injury were enrolled in the study. A homogeneous part of the bruise was irradiated first with a 5 ms pulse at 532 nm and then with a 5 ms pulse at 1064 nm. The resulting transient surface temperature change was collected with a fast IR camera. The initial temperature-depth profiles were reconstructed by solving the ill-posed inverse problem using a custom reconstruction algorithm. The PPTR signals and reconstructed initial temperature profiles showed that the 532 nm wavelength probed the shallow skin layers revealing moderate changes during bruise development, while the 1064 nm wavelength provided additional information for severe bruises, in which swelling was present. Our two-wavelength approach has the potential for an improved estimation of the bruise age, especially if combined with modeling of bruise dynamics.

Novel chairside spectrometer-trained system for measuring the irradiance of light-curing units.

The purpose of this study was to compare the performances of 5 different instruments in measuring the irradiance of light-curing units (LCUs). A novel spectrometer-trained radiometer (CheckUp), 2 conventional chairside radiometers (Bluephase Meter I and Bluephase Meter II), and 2 devices considered to be gold standards for measuring irradiance (an integrating sphere spectrometer and a thermopile sensor) were used to evaluate 7 LCUs. The irradiance of each LCU was measured 10 times with each meter. Data were analyzed using linear regression analysis and a 1-way analysis of variance with Tukey post hoc test (α = 0.05). The mean irradiance values of the LCUs differed significantly depending on which meter was used for measurement (P < 0.05). Bivariate regression analysis demonstrated that the highest correlations in the irradiance values were found between the CheckUp meter and both the integrating sphere (r2 = 0.980) and the thermopile (r2 = 0.933). The absolute mean (SD) percentage deviation between irradiance measured by the CheckUp instrument and irradiance measured by the other meters was 7.2% (2.0%) for the integrating sphere, 7.0% (3.6%) for the thermopile, 21.5% (16.1%) for Bluephase Meter I, and 13.1% (7.1%) for Bluephase Meter II. Compared with the 2 conventional chairside radiometers, the CheckUp meter provided the highest correlation with and lowest absolute percentage deviation from the irradiance measured by the gold standard spectrometers.

Night-sky radiometry can revolutionize the characterization of light-pollution sources globally.

The city emission function (CEF), describing the angular emission from an entire city as a light source, is one of the key elements in night-sky radiance models. The CEF describes the rate at which skyglow depends on distance and is indispensable in any prediction of light-pollution propagation into nocturnal environments. Nevertheless, the CEF remains virtually unexplored because appropriate retrieval tools have been unavailable until very recently. A CEF has now been obtained from ground-based night-sky observations and establishes an experiment successfully conducted in the field to retrieve the angular emission function for an urban area. The field campaign was conducted near the city of Los Mochis, Mexico, which is well isolated from other cities and thus dominates all light emissions in its vicinity. The experiment has proven that radiometry of a night sky can provide information on the light output pattern of a distant city and allows for systematic, full-area, and cost-efficient CEF monitoring worldwide. A database of CEFs could initiate a completely new phase in light-pollution research, with significant economy and advanced accuracy of night-sky brightness predictions. The experiment and its interpretation represent unique progress in the field and contribute to our fundamental understanding of the mechanism by which direct and reflected uplight interact while forming the CEF.

Achievement of 0.005 % combined transfer uncertainties in the NIST detector calibration facility.

Improvements in a lamp-monochromator-based facility at the National Institute of Standards and Technology (NIST), the Visible near-infrared Spectral Comparator Facility (VisSCF) which is used to calibrate optical detectors for spectral radiant power responsivity from 300 nm to 1100 nm, are described. These changes include extending the VisSCF operational range down to 300 nm from 350 nm, thereby fully covering the ultraviolet-A (UVA) spectral region and partially covering the UVB range. These improvements have lowered the magnitudes of most of the components in the uncertainty budget and have led to combined 0.005 % transfer (k=1) uncertainties in the spectral power responsivity calibrations over most of the spectral range. Redevelopment of the uncertainty budget results in total expanded uncertainties of spectral responsivities of less than 0.1 % (k=2) over the spectral range from 380 nm to 980 nm, with the greatest uncertainty term coming from the calibrations of the transfer standards.

Correction of Radiometry Data for Temperature Effect on Dark Current, with Application to Radiometers on Profiling Floats.

Measurements of daytime radiometry in the ocean are necessary to constrain processes such as photosynthesis, photo-chemistry and radiative heating. Profiles of downwelling irradiance provide a means to compute the concentration of a variety of in-water constituents. However, radiometers record a non-negligible signal when no light is available, and this signal is temperature dependent (called the dark current). Here, we devise and evaluate two consistent methods for correction of BGC-Argo radiometry measurements for dark current: one based on measurements during the day, the other based on night measurements. A daytime data correction is needed because some floats never measure at night. The corrections are based on modeling the temperature of the radiometer and show an average bias in the measured value of nearly 0.01 W m-2 nm-1, 3 orders of magnitude larger than the reported uncertainty of 2.5×10-5 W m-2 nm-1 for the sensors deployed on BGC-Argo floats (SeaBird scientific OCR504 radiometers). The methods are designed to be simple and robust, requiring pressure, temperature and irradiance data. The correction based on nighttime profiles is recommended as the primary method as it captures dark measurements with the largest dynamic range of temperature. Surprisingly, more than 28% of daytime profiles (130,674 in total) were found to record significant downwelling irradiance at 240-250 dbar. The correction is shown to be small relative to near-surface radiance and thus most useful for studies investigating light fields in the twilight zone and the impacts of radiance on deep organisms. Based on these findings, we recommend that BGC-Argo floats profile occasionally at night and to depths greater than 250 dbar. We provide codes to perform the dark corrections.

High amplification laser-pressure optic enables ultra-low uncertainty measurements of the optical laser power at kilowatt levels.

We present the first measurements of kilowatt laser power with an uncertainty less than 1 %. These represent progress toward the most accurate measurements of laser power above 1 kW at 1070 nm wavelength and establish a more precise link between force metrology and laser power metrology. Radiation pressure, or photon momentum, is a relatively new method of non-destructively measuring laser power. We demonstrate how a multiple reflection optical system amplifies the pressure of a kilowatt class laser incoherently to improve the signal to noise ratio in a radiation pressure-based measurement. With 14 incoherent reflections of the laser, we measure a total uncertainty of 0.26 % for an input power of 10 kW and 0.46 % for an input power of 1 kW at the 95 % confidence level. These measurements of absolute power are traceable to the SI kilogram and mark a state-of-the-art improvement in measurement precision by a factor of four.

Correction of Biogeochemical-Argo Radiometry for Sensor Temperature-Dependence and Drift: Protocols for a Delayed-Mode Quality Control.

Measuring the underwater light field is a key mission of the international Biogeochemical-Argo program. Since 2012, 0-250 dbar profiles of downwelling irradiance at 380, 412 and 490 nm besides photosynthetically available radiation (PAR) have been acquired across the globe every 1 to 10 days. The resulting unprecedented amount of radiometric data has been previously quality-controlled for real-time distribution and ocean optics applications, yet some issues affecting the accuracy of measurements at depth have been identified such as changes in sensor dark responsiveness to ambient temperature, with time and according to the material used to build the instrument components. Here, we propose a quality-control procedure to solve these sensor issues to make Argo radiometry data available for delayed-mode distribution, with associated error estimation. The presented protocol requires the acquisition of ancillary radiometric measurements at the 1000 dbar parking depth and night-time profiles. A test on >10,000 profiles from across the world revealed a quality-control success rate >90% for each band. The procedure shows similar performance in re-qualifying low radiometry values across diverse oceanic regions. We finally recommend, for future deployments, acquiring daily 1000 dbar measurements and one night profile per year, preferably during moonless nights and when the temperature range between the surface and 1000 dbar is the largest.

Statistical Characterization of Temperature and Pressure Vertical Profiles for the Analysis of Laser Heterodyne Radiometry Data.

The statistical analysis of historic pressure and temperature profiles from radiosonde launches for use in the fitting of molecular oxygen line shapes is presented. As the O2 mixing ratio is nearly constant throughout the lower atmosphere, only variations in pressure and temperature profiles will affect the fit of observed O2 features in Laser Heterodyne Radiometry (LHR) spectra. Radiosonde temperature and pressure data are extracted from the Integrated Global Radiosonde Archive (IGRA) for a given station, date, and launch time. Data may be extracted for a single launch, for the same date over several years, and/or within a window centered on a target date. The temperature and pressure profiles are further characterized by the statistical variation in coefficients of polynomial fits in altitude. The properties of the probability distributions for each coefficient are used to constrain fits of O2 line shapes through Nelder-Mead optimization. The refined temperature and pressure profiles are then used in the retrieval of vertically resolved mixing ratios for greenhouse gases (GHGs) measured in the same instrument. In continuous collections, each vertical profile determination may be treated as a Bayesian prior to inform subsequent measurements and provide an estimate of uncertainties.

Thermal Imaging Metrology Using High Dynamic Range Near-Infrared Photovoltaic-Mode Camera.

The measurement of a wide temperature range in a scene requires hardware capable of high dynamic range imaging. We describe a novel near-infrared thermal imaging system operating at a wavelength of 940 nm based on a commercial photovoltaic mode high dynamic range camera and analyse its measurement uncertainty. The system is capable of measuring over an unprecedently wide temperature range; however, this comes at the cost of a reduced temperature resolution and increased uncertainty compared to a conventional CMOS camera operating in photodetective mode. Despite this, the photovoltaic mode thermal camera has an acceptable level of uncertainty for most thermal imaging applications with an NETD of 4-12 °C and a combined measurement uncertainty of approximately 1% K if a low pixel clock is used. We discuss the various sources of uncertainty and how they might be minimised to further improve the performance of the thermal camera. The thermal camera is a good choice for imaging low frame rate applications that have a wide inter-scene temperature range.

Noninvasive Monitoring of Dynamical Processes in Bruised Human Skin Using Diffuse Reflectance Spectroscopy and Pulsed Photothermal Radiometry.

We have augmented a recently introduced method for noninvasive analysis of skin structure and composition and applied it to monitoring of dynamical processes in traumatic bruises. The approach combines diffuse reflectance spectroscopy in visible spectral range and pulsed photothermal radiometry. Data from both techniques are analyzed simultaneously using a numerical model of light and heat transport in a four-layer model of human skin. Compared to the earlier presented approach, the newly introduced elements include two additional chromophores (ß-carotene and bilirubin), individually adjusted thickness of the papillary dermal layer, and analysis of the bruised site using baseline values assessed from intact skin in its vicinity. Analyses of traumatic bruises in three volunteers over a period of 16 days clearly indicate a gradual, yet substantial increase of the dermal blood content and reduction of its oxygenation level in the first days after injury. This is followed by the emergence of bilirubin and relaxation of all model parameters towards the values characteristic for healthy skin approximately two weeks after the injury. The assessed parameter values and time dependences are consistent with existing literature. Thus, the presented methodology offers a viable approach for objective characterization of the bruise healing process.

High Performance Predictable Quantum Efficient Detector Based on Induced-Junction Photodiodes Passivated with SiO2/SiNx.

We performed a systematic study involving simulation and experimental techniques to develop induced-junction silicon photodetectors passivated with thermally grown SiO2 and plasma-enhanced chemical vapor deposited (PECVD) SiNx thin films that show a record high quantum efficiency. We investigated PECVD SiNx passivation and optimized the film deposition conditions to minimize the recombination losses at the silicon-dielectric interface as well as optical losses. Depositions with varied process parameters were carried out on test samples, followed by measurements of minority carrier lifetime, fixed charge density, and optical absorbance and reflectance. Subsequently, the surface recombination velocity, which is the limiting factor for internal quantum deficiency (IQD), was obtained for different film depositions via 2D simulations where the measured effective lifetime, fixed charge density, and substrate parameters were used as input. The quantum deficiency of induced-junction photodiodes that would be fabricated with a surface passivation of given characteristics was then estimated using improved 3D simulation models. A batch of induced-junction photodiodes was fabricated based on the passivation optimizations performed on test samples and predictions of simulations. Photodiodes passivated with PECVD SiNx film as well as with a stack of thermally grown SiO2 and PECVD SiNx films were fabricated. The photodiodes were assembled as light-trap detector with 7-reflections and their efficiency was tested with respect to a reference Predictable Quantum Efficient Detector (PQED) of known external quantum deficiency. The preliminary measurement results show that PQEDs based on our improved photodiodes passivated with stack of SiO2/SiNx have negligible quantum deficiencies with IQDs down to 1 ppm within 30 ppm measurement uncertainty.

Spatially Resolved Analysis of Urban Thermal Environments Based on a Three-Dimensional Sampling Algorithm and UAV-Based Radiometric Measurements.

A new method and workflow to assess outdoor thermal comfort and thermal stress in urban areas is developed. The new methodology is applied to a case of an urban quarter in the city of Graz. The method recognises the significance of detailed and accurate spatially resolved determination of mean radiant temperatures taking into account all relevant radiative components, comprising thermal radiation, as well as global radiation. The method relies on radiometric imaging data that are mapped onto a three-dimensional model. The image data are acquired by means of drones (UAVs) equipped with multispectral and thermographic cameras to capture short- and long-wave radiation. Pre-existing city models and a Monte Carlo raytracing algorithm to perform anisotropic sampling based on a 3D model with human topology are used to determine local radiation temperatures with high spatial resolution. Along with spot measurements carried out on the ground simultaneously, the spatially resolved and three-dimensionally determined mean radiation temperatures are used to calculate thermal comfort indicator maps using UTCI and PMV calculation. Additional ground measurements are further used to validate the detection, as well as the entire evaluation process.

Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 µm to 20 µm wavelength.

We have constructed, calibrated, and tested a cryogenic low-background infrared radiometer for both spectral radiance and irradiance measurements over the 4 µm to 20 µm wavelength range. The primary purpose of the Missile Defense Transfer Radiometer (MDXR) is to measure absolute irradiance or radiance from cryogenic infrared test chamber sources using a photoconductive Si:As Blocked Impurity Band (BIB) detector and a set of spectral filters. The MDXR also includes an absolute cryogenic radiometer (ACR) and a Fourier transform spectrometer (FTS). For irradiance measurements, the ACR is used to provide the primary power scale for the BIB detector in conjunction with spectral filters, while the FTS/BIB configuration derives its scale from an internal blackbody source. The two measurement scales show agreement for the irradiance of highly collimated (< 1 mrad) infrared beams from 10-13 W/µm/cm2 to 10-8 W/µm/cm2 within the combined relative uncertainties of 2.6 % (coverage factor k = 1.) We have also calibrated the radiometer for radiance measurements by using a large cavity fluid bath blackbody that overfills the spatial and angular extent of the radiometer entrance pupil. The radiometric calibration uncertainty analysis of the radiometer as well as its maintenance and stability are discussed.

Joint microwave radiometry for inflammatory arthritis assessment.

OBJECTIVES: Increased in-depth joint temperature measured by the rapid, easy-to-perform microwave radiometry (MWR) method may reflect inflammation, even in the absence of clinical signs. We hypothesized that MWR is useful for RA and spondyloarthritis patients' assessment. METHODS: Clinical examination, joint ultrasound and/or MRI and MWR were performed in two independent patient-control cohorts (n = 243). RESULTS: Among single RA joints MWR performed best in the knee using ultrasound as reference, with 75% sensitivity-73% specificity for grey-scale synovitis score ⩾2, and 80% sensitivity-82% specificity for power Doppler positivity. A stronger agreement was evident between increased knee relative temperature (Δt) and power Doppler positivity (82%) than with clinical examination (76%). In a different patient cohort with painful knees, a knee Δt ⩽0.2 predicted power Doppler positivity with 100% positive and negative predictive values. A thermo-score summing 10 Δt values of three large and seven small RA joints (elbow, knee, ankle, wrist, four hand and two foot joints of the clinically dominant arm or hand and leg or foot) correlated with ultrasound scores of synovitis/tenosynovitis (all P < 0.001) and the 28-joint Disease Activity Score (DAS28) (P = 0.004). The agreement of the thermo-score with ultrasound-defined joint inflammation (82%) was stronger than with DAS28 (64%). The thermo-score improved significantly after 90 days of treatment in patients with active RA at baseline (P = 0.004). Using MRI as reference, Δt of sacroiliac joints could discriminate between spondyloarthritis patients with or without sacroiliitis with 78% sensitivity-74% specificity. CONCLUSION: In-depth increased MWR-derived joint temperature reflects both subclinical and clinically overt inflammation and may serve as a biomarker in arthritis.

The Reflectance of Human Skin in the Millimeter-Wave Band.

The millimeter-wave band is an ideal part of the electromagnetic radiation to diagnose human skin conditions because this radiation interacts only with tissue down to a depth of a millimetre or less over the band range from 30 GHz to 300 GHz. In this paper, radiometry is used as a non-contact sensor for measuring the human skin reflectance under normal and wet skin conditions. The mean reflectance of the skin of a sample of 50 healthy participants over the (80-100) GHz band was found to be ~0.615 with a standard deviation of ~0.088, and an experimental measurement uncertainty of ±0.005. The thinner skin regions of the back of the hand, the volar forearms and the inner wrist had reflectances 0.068, 0.068 and 0.062 higher than the thicker skin regions of the palm of the hand, the dorsal forearm and the outer wrist skin. Experimental measurements of human skin reflectance in a normal and a wet state on the back of the hand and the palm of the hand regions indicated that the mean differences in the reflectance before and after the application of water were ~0.078 and ~0.152, respectively. These differences were found to be statistically significant as assessed using t-tests (34 paired t-tests and six independent t-tests were performed to assess the significance level of the mean differences in the reflectance of the skin). Radiometric measurements in this paper show the quantitative variations in the skin reflectance between locations, sexes, and individuals. The study reveals that these variations are related to the skin thickness and water content, a capability that has the potential to allow radiometry to be used as a non-contact sensor to detect and monitor skin conditions such as eczema, psoriasis, malignancy, and burn wounds.