Blackbody Source Research Articles

Fast Variable-Temperature Cryogenic Blackbody Sources for Calibration of THz Superconducting Receivers

An electrically heated blackbody radiation source comprising thin metal film on a dielectric substrate and an integrating cavity was designed, fabricated, and experimentally studied at frequencies from 75 to 500 GHz. Analytical and numerical modeling were performed to optimize the emissivity, spectral uniformity, and modulation frequency of the radiation source with the spherical integrating cavity and thin film absorber. The blackbody emissivity (absorptivity) increased from 0.3 to 0.5 for the bare thin film on dielectric substrate, and up to 0.95 when it was placed inside the integrating cavity. The fabricated source mounted at the 0.5 K stage was used to measure the response time of a few microseconds and for sensitivity measurement down to 10−18 W/Hz1/2 of the superconductor–insulator–normal metal–insulator–superconductor (SINIS) detector at 100 mK.

Evaluation of laboratory accuracy of forehead radiation thermometers using blackbody sources for tympanic thermometers defined by international standards with adaptors

In view of the gaps between the current clinical thermometer standards and the commercially available products, in particular the introduction of forehead radiation thermometers into the market, ISO initiated a review on standard for clinical thermometers. The original clinical thermometer standard includes requirements for evaluating tympanic (ear) thermometers using identified reference blackbody sources. However, one of the challenges in reviewing the standard is to understand if the reference blackbody sources identified for ear thermometers are still usable for evaluating the laboratory accuracy of forehead thermometers. In order to answer this challenge, four brand new forehead thermometers from two different manufacturers are evaluated at NMC. Two reference blackbody sources, one JIS standard source with very small opening and one NMC source with larger opening, are used for the evaluation. In order to use JIS standard source, two types of adaptors, one supplied by one of the manufactures, one 3D printed, are evaluated. The measurement results together with their measurement uncertainties are presented and analysed. Suitable adaptors are identified and recommended.

Thermal Noise Measurements in a Reverberation Chamber

Two models describing properties of the thermal noise power emerging from an antenna mounted in a reverberation chamber are described. The first compares the reverberation chamber to an over-molded cavity acting as a black-body source; the second describes the noise in terms of the antenna noise temperature. Measurements based on the antenna noise temperature model show the noise power to be dependent on the position of the rotating mechanical stirrer. The correlation of the antenna noise temperature with the stirrer position-dependent antenna mismatch factor is shown. When a signal is injected into the chamber measurements of the signal to noise power ratio show that this ratio is dependent on the stirrer position and also the position of the signal source within the chamber. These results have significant consequences for the detection of weak signals from radiating sources in a reverberation chamber.

A temperature-controlled mid-wave infrared polarization radiation source with adjustable degree of linear polarization

This paper proposes a temperature-controlled mid-wave infrared polarization radiation source with adjustable degree of linear polarization (DoLP), referred to as TMPSD, which will be useful for the polarization performance measurements of the thermal polarization imaging systems. The main parts of the TMPSD are a standard blackbody source, a variable temperature cell holder and a mid-wave infrared polarizer placed in it. The experimental results show that when the temperature range of the blackbody source changes between 20 °C and 100 °C, and that of the polarizer between −120 °C and 20 °C, the DoLP of the radiation emitted from the TMPSD is 0.2683–0.9072 in the 3.0–5.2 μm bandwidth. The TMPSD exhibiting the large dynamic range and high accuracy can be readily adjusted. It is expected that the proposed TMPSD will effectively improve the quantitative accuracy of infrared polarization imaging systems during performance calibration and testing of mid-wave infrared polarization imaging systems.

Transient Thermal Characteristics of a Heated Infrared Temperature Sensor for Noncontact Medical Thermometry.

In this work, the transient responses of a heated infrared (IR) temperature sensor were investigated to improve the reliability of determined target temperatures obtained from IR-based medical thermometers. A medical-grade IR temperature sensor was heated at the lower edge of the sidewall of the sensor. To reduce the uncertainty due to the conversion factor of the thermal detector, the temperature of the target, which was a thermostatted blackbody source, was determined when the observed target temperature and the temperature of the detector coincided during the heating and cooling of the sensor. When the determined target temperature was compared with the blackbody source temperature, it was found that during heating, due to the produced temperature gradient in the sensor, the observed target temperature showed erroneous depressions, resulting in the determined target temperature being considerably lower than the true target temperature. In contrast, the determined target temperature during cooling of the heated sensor was consistent with the tested blackbody source temperatures within the claimed uncertainty at all heating conditions. Therefore, based on the obtained results, it was concluded that temperature measurements using an IR temperature sensor could be carried out with the least uncertainty by determining the target temperature when the observed target and detector temperatures coincided during cooling of the heated sensor.

The super-soft source phase of the recurrent nova V3890 Sgr

Context.The 30-yr recurrent symbiotic nova V3890 Sgr exploded on 2019 August 28 and was observed with multiple X-ray telescopes.Swiftand AstroSat monitoring revealed slowly declining hard X-ray emission from shocks between the nova ejecta and the stellar wind of the companion. Later, highly variable super-soft-source (SSS) emission was seen. AnXMM-Newtonobservation during the SSS phase captured the high degree of X-ray variability in terms of a deep dip in the middle of the observation.Aims.This observation adds to the growing sample of diverse SSS spectra and allows spectral comparison of low- and high-state emission to identify the origin of variations and subsequent effects of such dips, all leading to new insights into how the nova ejecta evolve.Methods.Based on an initial visual inspection, quantitative modelling approaches were conceptualised to test hypotheses of interpretation. The light curve was analysed with a power spectrum analysis before and after the dip and with an eclipse model to test the hypothesis of occulting clumps as in U Sco. A phenomenological spectral model (SPEX) was used to fit the complex Reflection Grating Spectrometer (RGS) spectrum accounting for all known atomic physics. A blackbody source function was assumed, as in all atmosphere radiation transport models, while the complex radiation transport processes were not modelled. Instead, one or multiple absorbing layers were used to model the absorption lines and edges, taking into account all state-of-the-art knowledge of atomic physics.Results.In addition to the central deep dip, there is an initial rise of similar depth and shape, and, after the deep dip, there are smaller dips of ~10% amplitude, which might be periodic over 18.1-min. Our eclipse model of the dips yields clump sizes and orbital radii of 0.5–8 and 5–150 white dwarf radii, respectively. The simultaneousXMM-NewtonUV light curve shows no significant variations beyond slow fading. The RGS spectrum contains both residual shock emission at short wavelengths and the SSS emission at longer wavelengths. The shock temperature has clearly decreased compared to an earlierChandraobservation (day 6). The dip spectrum is dominated by emission lines as in U Sco. The intensity of underlying blackbody-like emission is much lower with the blackbody normalisation yielding a similar radius to that of the brighter phases, while the lower bolometric luminosity is ascribed to lowerTeff. This would be inconsistent with clump occultations unless Compton scattering of the continuum emission reduces the photon energies to mimic a lower effective temperature. However, systematic uncertainties are high. The absorption lines in the bright SSS spectrum are blueshifted by 870 ± 10 km s−1before the dip and are slightly faster, 900 ± 10 km s−1, after the dip. The reproduction of the observed spectrum is astonishing, especially that only a single absorbing layer is necessary while three such layers are needed to reproduce the RGS spectrum of V2491 Cyg. The ejecta of V3890 Sgr are thus more homogeneous than many other SSS spectra indicate. Abundance determination is in principle possible but highly uncertain. Generally, solar abundances are found, except for N and possibly O, which are higher by an order of magnitude.Conclusions.High-amplitude variability of SSS emission can be explained in several ways without having to give up the concept of constant bolometric luminosity. Variations in the photospheric radius can expose deeper lying plasma that could pulse with 18.1 min and that would yield a higher outflow velocity. Also, clump occultations are consistent with the observations.

The ω-absorption line distribution function for rank correlated SLW model prediction of radiative transfer in non-uniform gases

Unlike previous global methods, the recently developed Rank Correlated Spectral Line Weighted-sum-of-gray-gases (RC-SLW) model does not require specification of a reference gas thermodynamic state from which all other states are corrected using a correlated spectrum assumption. However, the RC-SLW approach still requires specification of an arbitrary blackbody source temperature to generate the Absorption Line Blackbody Distribution Function (ALBDF) used in construction of the spectral model. This paper reports on the development of a universal RC-SLW model that eliminates the need for the specification of a blackbody source temperature. The approach replaces the ALBDF with a new spectral distribution function, herein termed the ω-Absorption Line Distribution Function (ω-ALDF), and is based on a new spectral weighting function instead of the Planck blackbody distribution function. The ω-ALDF presented here depends only on the local gas thermodynamic state, and does not involve the blackbody source temperature used in the ALBDF. The new weighting function is determined using the well-established ALBDF, avoiding the need to generate a radically new distribution function database from the detailed gas absorption cross-section data. The ω-ALDF based RC-SLW model thus requires no user-specified parameters (no reference thermodynamic state and no blackbody source temperature). Further, only minor modification of the conventional RC-SLW model is needed to implement the new approach. Development of this new distribution function is only possible within the theoretical framework of the Rank Correlated SLW model. This work presents the theoretical development of the ω-ALDF, and demonstrates the use and accuracy of this new universal RC-SLW model.

Cryogenic blackbody calibration source for superconducting terahertz detectors

Blackbody radiation source has been widely used as a calibration source for terahertz (THz) radiometers in recent decades with the applications of THz detection technology in the fields of aerospace, astronomy and remote sensing. We develop a THz blackbody calibration source capable of working in the cryogenic environment and having adjustable radiation power for the calibration of THz superconducting detectors. The ideal blackbody source has an emissivity and absorptivity of 1 and the reflectance coefficient is used to indirectly characterise the performance of the developed blackbody source. In this work, we use a mixture of epoxy, catalyst, carbon black and glass beads as blackbody absorbing material. The real part and imaginary part of the complex dielectric constant of Berkeley blackbody material are extracted from the THz time-domain spectra, and its reflection coefficient is measured. We use this material to design a conical blackbody radiation source , and simulate it as well. The simulation result show that it has low reflectivity below –35 dB in a frequency range of 0.2–0.5 THz. We fabricate a conical blackbody radiation source that is mounted in a dilution refrigerator, and use filters and light-guiding systems to make the detector for measuring the radiation by the THz light of a specific wavelength. The radiation power can be tuned by changing its temperature. The relationship between radiation power and temperature shows a power tuning range of 10<sup>–12</sup>–10<sup>–9</sup> W in the frequency range of 0.2–0.5 THz with a minimum power value of 2.13 × 10<sup>–12</sup> W. The designed blackbody radiation source can meet the calibration requirements of THz superconducting detectors, and will contribute to the development and application of highly sensitive THz radiometers.

Experimental Research on the Temperature Characterization of a Miniature Phase Change Cells in the Blackbody for the On-Orbit Radiometric Calibration of Thermal Infrared Sensors

For on-orbit radiometric calibration of infrared (IR) satellite instruments, we have developed a blackbody source whose temperature can be accurately determined by use of miniature phase change cells to provide fixed points. The temperatures and reproducibility of six phase change cells containing H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, Ga–Sn alloy, Ga–Zn alloy, phenyl salicylate (PS), succinonitrile, and Ga were accurately determined by the measurement of the phase change plateaux. The points were measured using the quasiadiabatic vacuum measurement system, which was developed by the National Institute of Metrology, China. The reproducibility time span of the Ga fixed point was as long as six years. Results indicated that the reproducibility values of multiple phase-change run-off point temperatures of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O, Ga–Sn alloy, Ga–Zn alloy, PS, succinonitrile, and Ga were 2.0, 3.6, 1.5, 3.5, 2.9, and 3.1 mK, respectively. Furthermore, a strong linear relation was observed between the heating power and the run-off temperature. With decreasing heating power, the temperature of the plateau decreased and approached the defined fixed-point value. All simulation results of the miniature fixed points were consistent with the experimental data.

Photoacoustic simultaneous detection of multiple trace gases for industrial park application

The determination of toxic or harmful gases in industrial parks is a challenge to monitoring exhaust contaminants due to the features of complex compositions and ubiquity. Blackbody sources play an important role in simultaneously detecting the multiple gas species in the presence of cross-interfering absorption lines due to their effective ultra-wide wavelength range. Nevertheless, the problem of lower intensity per wavelength and less stability persists as an obstacle for highly sensitive trace gas detection. In this study, a dual optical path (DOP) enhanced differential photoacoustic and spectral detection mode is developed for simultaneously detecting the multiple toxic or harmful gas through augmenting the weak effective absorption signals and suppressing the spurious coherent background noise. Two identical T-type photoacoustic resonators are introduced to enable the differential mode. Neverthelss, the pure optical approach cannot distinguish the absorption characteristics of acetylene (C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;2&lt;/sub&gt;) with volume fraction 5 × 10&lt;sup&gt;–5&lt;/sup&gt; even with the DOP enhancement, whereas emerging peaks in the differential photoacoustic (PA) mode reveal the capability of PA spectroscopy to suppress coherent noise. The results demonstrate that the differential PA signal is improved by 1.91 times that obtained by the DOP design. Methane (NH&lt;sub&gt;3&lt;/sub&gt;), acetylene (C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;2&lt;/sub&gt;) and carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) are used to verify the performance of this DOP enhanced differential PA gas sensor, and the volume fraction of the sensitivity is found to be 7.25 × 10&lt;sup&gt;–7&lt;/sup&gt; for CO&lt;sub&gt;2&lt;/sub&gt;, 1.84 × 10&lt;sup&gt;–6&lt;/sup&gt; for C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;2&lt;/sub&gt;, and 1.43 × 10&lt;sup&gt;–6&lt;/sup&gt; for NH&lt;sub&gt;3&lt;/sub&gt; at standard temperature and pressure, which is an order of magnitude higher than the original single mode PA value. Linear PA amplitude responses ranging from 0 to 3 × 10&lt;sup&gt;–3&lt;/sup&gt; in volume fraction with respect to the three target gases are observed, and the correction coefficients are all greater than 0.995. The DOP enhanced differential PA detection mode compensates for the weakness of the limited sensitivity associated with broadband spectroscopic methods based on blackbody radiator. Thus, the broadband DOP enhanced differential photoacoustic modality is demonstrated to be an effective approach to simultaneous, highly sensitive and selective detection of multiple trace gases.

A Practical Validation of Uncooled Thermal Imagers for Small RPAS

Uncooled thermal imaging sensors in the LWIR (7.5 μm to 14 μm) have recently been developed for use with small RPAS. This study derives a new thermal imaging validation methodology via the use of a blackbody source (indoors) and real-world field conditions (outdoors). We have demonstrated this method with three popular LWIR cameras by DJI (Zenmuse XT-R, Zenmuse XT2 and, the M2EA) operated by three different popular DJI RPAS platforms (Matrice 600 Pro, M300 RTK and, the Mavic 2 Enterprise Advanced). Results from the blackbody work show that each camera has a highly linearized response (R2 &gt; 0.99) in the temperature range 5–40 °C as well as a small (&lt;2 °C) temperature bias that is less than the stated accuracy of the cameras. Field validation was accomplished by imaging vegetation and concrete targets (outdoors and at night), that were instrumented with surface temperature sensors. Environmental parameters (air temperature, humidity, pressure and, wind and gusting) were measured for several hours prior to imaging data collection and found to either not be a factor, or were constant, during the ~30 min data collection period. In-field results from imagery at five heights between 10 m and 50 m show absolute temperature retrievals of the concrete and two vegetation sites were within the specifications of the cameras. The methodology has been developed with consideration of active RPAS operational requirements.

Thermal Sensor Calibration for Unmanned Aerial Systems Using an External Heated Shutter

Uncooled thermal infrared sensors are increasingly being deployed on unmanned aerial systems (UAS) for agriculture, forestry, wildlife surveys, and surveillance. The acquisition of thermal data requires accurate and uniform testing of equipment to ensure precise temperature measurements. We modified an uncooled thermal infrared sensor, specifically designed for UAS remote sensing, with a proprietary external heated shutter as a calibration source. The performance of the modified thermal sensor and a standard thermal sensor (i.e., without a heated shutter) was compared under both field and temperature modulated laboratory conditions. During laboratory trials with a blackbody source at 35 °C over a 150 min testing period, the modified and unmodified thermal sensor produced temperature ranges of 34.3–35.6 °C and 33.5–36.4 °C, respectively. A laboratory experiment also included the simulation of flight conditions by introducing airflow over the thermal sensor at a rate of 4 m/s. With the blackbody source held at a constant temperature of 25 °C, the introduction of 2 min air flow resulted in a ’shock cooling’ event in both the modified and unmodified sensors, oscillating between 19–30 °C and -15–65 °C, respectively. Following the initial ‘shock cooling’ event, the modified and unmodified thermal sensor oscillated between 22–27 °C and 5–45 °C, respectively. During field trials conducted over a pine plantation, the modified thermal sensor also outperformed the unmodified sensor in a side-by-side comparison. We found that the use of a mounted heated shutter improved thermal measurements, producing more consistent accurate temperature data for thermal mapping projects.

Implications for accurate surface temperature monitoring in powder bed fusion: Using multi-wavelength pyrometry to characterize spectral emissivity during processing

Radiation thermometry methods used in powder bed fusion (PBF) additive manufacturing for in situ monitoring and control and quality assurance are increasing in importance. Arguably, the most significant challenge associated with radiation thermometry methods is the limited understanding of the emissivity, that is the emissive behavior of the entire region being measured. This work describes a new approach for measuring the emissive behaviors of PBF materials during processing using a multi-wavelength (MW) or Spectropyrometer operating in the spectral range from 1000 to 1650 nm. The approach was implemented in an electron beam (EB) PBF machine, using the electron beam as a heat source, allowing for (1) measuring spectral emissive behavior of the surface in a fixed small region (~2.65 mm) throughout a variety of dynamic processing conditions including heating, melting, and cooling; (2) controlling the scanning (heating) profile during processing while rejecting radiative interference in the measurements due to heating lasers (~1070 nm) commonly used in laser PBF; and (3) processing in an evacuated environment to assist with reduction of additional environmental effects that could impact the measurements. The experimental setup included a sight tube that prevented both metallization of the viewport and resultant signal decay, which enabled near-continuous measurements throughout processing. Measurements from the MW pyrometer were compared against those of a type K thermocouple that was placed in the vicinity of the measurement area. Prior to the powder bed preheating experiment, the MW pyrometer was calibrated against a NIST traceable blackbody source. The utility of the approach was demonstrated by acquiring measurements from the surface of a copper (d50~75 µm) powder bed that was progressively heated in a series of nine steps inside an Arcam A2 EB-PBF system through scanning with the electron beam. Following the preheat steps, seven consecutive melt steps were implemented enabling measurements of the emissive behavior for copper during its multiple solid-liquid-solid transitions. The unique capabilities of the MW pyrometer provided measured values of emissivity of copper that exhibited temporal, spectral (1080–1640 nm) and thermal dependence, verifying the non-graybody behavior for copper. Ongoing work will demonstrate the applicability of this technique across multiple powder metal alloy systems and PBF technologies.

Design & simulation of high temperature blackbody source for calibration of Michelson interferometer ECE diagnostic

This paper presents the design, simulation and characterization of a high temperature black body source for a target temperature of 873 K and frequency range of 70 to 143 GHz. The high temperature black body source has been designed using CST Microwave Studio. Different solvers in CST have been used to determine various black body parameters such as scattering, emissivity, reflectivity, radiation intensity, temperature distribution etc. This work consists of two novel approaches. First, the emissivity values have been calculated from the simulation results. Second, the design and optimization of the emitter and heater surface has been carried out separately and finally integrated to form the black body source. After sufficient study & literature survey, silicon carbide was selected as a suitable material for emitter and molybdenum for heater. The design comprises of a pyramidal moth eye structure made up of silicon carbide. Design and simulations were carried out with different dimensions of pyramids by varying their slant angle and height. The thickness of the silicon carbide base plate has also been varied to achieve optimal performance. Selection of best design is done by comparing results of radiation intensity, emissivity and temperature gradient of various simulated models. The design aimed to obtain the emissivity values near to unity with uniform temperature distribution across the emitter surface. Significant improvement in emissivity values were obtained by multiple changes in the heater and emitter design. The designed source after fabrication will be used as a high temperature calibration source for Michelson interferometer system serving as an electron cyclotron emission (ECE) diagnostic at IPR.

Accurate Clinical Tympanic Thermometer Measurement System at NMISA

Infrared ear thermometers allow users to measure body temperature quickly and non-invasively by inserting a probe into the patient’s ear canal. The effectiveness of tympanic ear thermometers is dependent on how accurate their measurement is. This prompts the demand for accurate and reliable calibration of ear thermometers. Developing capability and providing traceability to the health care facilities in South Africa have become crucial, as there is no calibration laboratory that provides such a service. A standard ear-thermometer black-body source system that is traceable to ITS-90 temperature has been constructed and assembled at the NMISA temperature laboratory. The ITS-90-traceable measurement system developed has a measuring capability of 40 mK (k=2) to 70 mK (k=2) in the temperature range of 35.5 °C to 41.5 °C. At the human body temperature of 37 °C an uncertainty of 45 mK (k=2) is achieved.

Performance characterization of non-contact infrared thermometers (NCITs) for forehead temperature measurement

The ability to assess the performance of a non-contact infrared thermometer (NCIT) may be limited due to the algorithms necessary to predict a reference site temperature (e.g., oral) from a measurement of the forehead skin temperature. The algorithm not only adjusts for the difference between the reference site temperature and forehead temperature, but may also account for hardware corrections, bias adjustments and emissivity settings. These algorithms are proprietary to the manufacturer and can be unique for each device. ASTM E1965-98 (2016) is a standard test method for the evaluation of NCITs. It includes forehead thermometers; however, the algorithm must be known or an unadjusted calibration mode must be accessible. This study evaluates 6 NCIT models (10 units of each) against the ASTM standard error criterion using a blackbody source. Units were tested within the manufacturer's operating and temperature measurement range specification. A method to evaluate measurement outliers and characterize each model's performance when the adjustment algorithm is unknown is proposed. Using this method, 5 of the 6 models had a predicted error > 0.3°C.

Derivation of the final OSIRIS-REx OVIRS in-flight radiometric calibration

The OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) operates over the ∼0.4- to 4.3-μm wavelength range. Radiometric calibration over this broad range requires the use of multiple calibration sources. Initial OVIRS in-flight calibration coefficients were previously computed using ground calibration from visible integrating sphere and IR blackbody sources, cross-calibrated with Earth-observing satellites for visible wavelengths, and adjusted using the spectrum of the OSIRIS-REx mission’s target body, asteroid (101955) Bennu. As part of the final in-flight calibration, we determined that the best calibration method removes out-of-band IR signal leakage prior to radiometric calibration and updated the calibration coefficients accordingly. These final calibration coefficients work well for data where the field of view is filled, and we document the possible artifacts in underfilled spots.

A wavelength-scale black phosphorus spectrometer

On-chip spectrometers with compact footprints are being extensively investigated owing to their promising future in critical applications such as sensing, surveillance and spectral imaging. Most existing miniaturized spectrometers use large arrays of photodetection elements to capture different spectral components of incident light, from which its spectrum is reconstructed. Here, we demonstrate a mid-infrared spectrometer in the 2–9 µm spectral range, utilizing a single tunable black phosphorus photodetector with an active area footprint of only 9 × 16 µm2, along with a unique spectral learning procedure. Such a single-detector spectrometer has a compact size at the scale of the operational wavelength. Leveraging the wavelength and bias-dependent responsivity matrix learned from the spectra of a tunable blackbody source, we reconstruct unknown spectra from their corresponding photoresponse vectors. Enabled by the strong Stark effect and the tunable light–matter interactions in black phosphorus, our single-detector spectrometer shows remarkable potential in the reconstruction of the spectra of both monochromatic and broadband light. Furthermore, its ultracompact structure that is free from bulky interferometers and gratings, together with its electrically reconfigurable nature, may open up pathways towards on-chip mid-infrared spectroscopy and spectral imaging. A single-photodetector spectrometer based on black phosphorus is demonstrated in the wavelength range from 2 to 9 μm. The footprint is 9 × 16 μm2. The spectrometer is free from bulky interferometers and gratings, and is electrically reconfigurable.

Performance of an uncooled imaging interferometric spectrometer with intrinsic background radiation

A signal-to-noise performance of an imaging Michelson interferometer based on corner cubes is modeled and experimental results are presented. The influence from the background radiation of the uncooled sensor is explained. The noise equivalent spectral radiance is determined in the 700 to 1300 cm − 1 range at two spectral resolutions using blackbody sources. The performance of the sensor system is tested on a scene at an average temperature of 19°C. From these results, the performance is given in terms of number of samples and spectral resolution. The performance model is used to predict the sensor performance at different scene temperatures.

Sensor calibration impacts on dust detection based on MODIS and VIIRS thermal emissive bands

Dust detection using remotely sensed measurements has been one of the challenging problems encountered by atmospheric scientists. MODerate Resolution Imaging Spectroradiometer (MODIS) on the Terra (T) and Aqua (A) platforms have been a versatile sensor for well over 21 and 18 years respectively, and have been extremely useful in the retrieval of aerosol information over the entire globe. The MODIS radiances from the Level 1B in general are expected to be within 5% accuracy in the reflective wavelengths and within 1% in the thermal emissive wavelengths. In this paper, we evaluate the sensitivity of previously developed dust detection technique based on thermal emissive wavelengths, which correspond to MODIS bands 20, 29, 31, and 32 respectively. The Thermal Emissive Dust Index (TEDI) performed very comparably to the traditional Aerosol Optical Thickness (AOT) retrievals by MODIS reflective channels. Since the MODIS Thermal Emissive Bands (TEB) are well calibrated on-orbit using a BlackBody (BB) source, the calibration of these long wave infrared bands is quite robust. As A-MODIS continues to perform well beyond its designed lifetime of 6 years, the instrument has undergone various levels of degradation during its mission time. As a consequence, it is imperative to check the impacts of calibration on the higher-level retrievals. In this paper, we rigorously analyze the sensitivity of TEDI due to the impact of calibration by the afore-mentioned TEB. The perturbation of the dominant (linear) calibration term demonstrated the following: first, there was a correlation in the sensitivity of the TEDI due to the uncertainty in the linear calibration term. Based on a perturbation in the linear calibration term for all aforementioned bands over a range of ±5% yielded the TEDI sensitivity to vary from approximately −3.2% to about −3.6%. When considering the uncertainty in each individual band significant changes were observed. The least change was observed for the perturbation in the calibration of band 20 with the TEDI sensitivity and the largest sensitivity in TEDI was observed in the perturbation of band 31 calibration. Thus, in the case of TEDI, noticeable sensitivity due to calibration uncertainty was observed in bands 29, 31, and 32, reiterating the importance of the TEB calibration in these bands. Also, the dust detection scheme based on A-MODIS was successfully transferred to the follow-on sensors such as Suomi (SNPP) and NOAA 20 (N20) VIIRS. The results presented in this paper would be extremely helpful in understanding impacts of calibration on the higher-level products for both current and future missions based on the MODIS heritage. Finally, the work also identifies the importance of radiometric fidelity in maintaining the accuracy of the dust detection. Results presented will show drastic improvement of the Saharan dust detection after the reduction of the electronic crosstalk in the 8.5 µm channel of T-MODIS.