The performance of the multispectral thermal imager (MTI) surface temperature retrieval algorithm at three sites

We present validation studies of MLS V2.2 and V3.3 water vapor (WV) and ozone profiles over the Tibetan Plateau (Naqu and Lhasa) and its adjacent region (Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within −2.2±15.7% (n=74) and 0.3±14.9% (n=75) in the stratosphere at and above 82.5 hPa. Accordingly, at 100 hPa, the altitude approaching the tropopuase height, differences are within 9.8±46.0% (n=18) and 23.0±45.8% (n=17), and they are within 21.5±90.6% (n=104) and 6.0±83.4% (n=99) in upper troposphere. The differences of MLS ozone are within −11.7±16.3% (n=135, V2.2) and 15.6±24.2% (n=305, V3.3) at and above 82.5 hPa. At 100 hPa, they are within −3.5±54.4% (n=27) and −8.7±41.6% (n=38), and within 18.0±79.1% (n=47) and 34.2±76.6% (n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 hPa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau “ozone valley” season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 hPa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.

Ground‐based temperature and water vapor profiling of the atmosphere of Mars point to large annual variations in the water vapor saturation altitude, or hygropause, of the entire low‐to middle‐latitude atmosphere, as forced by the elliptical Mars orbit [Clancy et al., 1996]. We examine the effects of such an annual variation in the hygropause altitude (from <10 km to >30 km) on the photochemistry of the Mars atmosphere. The one‐dimensional, diffusive transport photochemical model of Nair et al. [1994] is run in a diurnally averaged mode for time‐dependent calculations of the annual behavior of Mars photochemistry at low to middle latitudes. The model incorporates a specified annual variation of the water vapor profile, based on the microwave observations of Mars water vapor and temperature profiles versus season (solar longitude, Ls). Due to their long photochemical lifetimes, Mars CO and O2 are expected and found to be in significant non‐equilibrium with the annually varying water vapor (and hence HOx) densities, and to present nearly constant abundances representative of the annual average water vapor profile. In contrast, Mars O3 has a photochemical lifetime of hours, and exhibits very large annual variations in response to the annual variation in the hygropause altitude. The global‐scale abundance of O3 at altitudes of 20–40 km is predicted to vary from >109 cm−3 around Mars aphelion (northern spring/summer, Ls = 71°) to ∼108 cm−3 around Mars perihelion (southern spring/summer, Ls = 251°). These model ozone variations are discussed in the context of the disparate Mars 5 (1974 [Krasnopolsky and Parshev, 1979]) and Phobos (1989 [Blamont and Chassefière, 1993]) measurements of low‐latitude ozone densities at 35–50 km altitude, as well as Hubble space telescope observations of enhanced low‐latitude ozone during the 1995 aphelion of Mars [Clancy et al., this issue].

Abstract. Ground-based microwave measurements performed at water vapor and oxygen absorption line frequencies are widely used for remote sensing of tropospheric water vapor density and temperature profiles, respectively. Recent work has shown that Bayesian optimal estimation can be used for improving accuracy of radiometer retrieved water vapor and temperature profiles. This paper focuses on using Bayesian optimal estimation along with time series of independent frequency measurements at K- and V-bands. The measurements are used along with statistically significant but short background data sets to retrieve and sense temporal variations and gradients in water vapor and temperature profiles. To study this capability, the Indian Institute of Tropical Meteorology (IITM) deployed a microwave radiometer at Mahabubnagar, Telangana, during August 2011 as part of the Integrated Ground Campaign during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX-IGOC). In this study, temperature profiles for the first time have been estimated using short but statistically significant background information so as to improve the accuracy of the retrieved profiles as well as to be able to detect gradients. Estimated water vapor and temperature profiles are compared with those taken from the reanalysis data updated by the Earth System Research Laboratory, National Oceanic and Atmospheric Administration (NOAA), to determine the range of possible errors. Similarly, root mean square errors are evaluated for a month for water vapor and temperature profiles to estimate the accuracy of the retrievals. It is found that water vapor and temperature profiles can be estimated with an acceptable accuracy by using a background information data set compiled over a period of 1 month.

The global navigation satellite system (GNSS) water vapor tomography technique can retrieve high-quality water vapor profiles and holds significant potential for improving the performance of the initial three-dimensional water vapor field in numerical weather prediction (NWP). However, the empirical voxel-division method of GNSS water vapor tomography has been predominantly used before, and existing tomographic results are rarely incorporated into the NWP models due to the lack of a direct assimilation interface, which becomes the focus of this study. An adaptive voxel-division method for GNSS water vapor tomography is first proposed. The optimal horizontal and vertical steps of water vapor tomography are determined by introducing the principles of maximum grid coverage and the equal amount of layered water vapor. In addition, a two-step variational assimilation method has been developed to address the limitation of existing NWP models without a direct interface for assimilating GNSS water vapor tomographic results. The proposed water vapor tomography method and its application in the weather research and forecasting (WRF) model are comprehensively analysed and evaluated. Numerical results in Hong Kong show the superior performance of the proposed adaptive voxel-division method for GNSS water vapor tomography compared with empirical methods. The average improvement rate of the root mean square error (RMSE) in the water vapor profile ranges from 10.6% to 48.7%, while that in the integrated water vapor is 19.0%–42.9%. Furthermore, the assimilated and forecasted results of assimilating GNSS tomographic results under different weather conditions are validated and proved the significantly positive contributions of water vapor profiles to the WRF model. Specifically, the RMSE reduction in precipitation is 43.5%, while that for relative humidity, temperature, and pressure are 50.7%/58.2%, 41.1%/48.3%, and 24.2%/33.7%, respectively, under no-rain and rain conditions compared with the traditional assimilation method. These results show the good performance of the proposed adaptive voxel-division method for water vapor tomography and the two-step method for assimilating the tomographic water vapor profile, which highlight the significant potential of the GNSS tomographic result for data assimilation.

Surface temperatures are estimated with high precision based on a multitemperature method for Fourier-transform spectrometers. The method is based on Planck's radiation law and a nonlinear least-squares fitting algorithm applied to two or more spectra at different sample temperatures and a single measurement at a known sample temperature, for example, at ambient temperature. The temperature of the sample surface can be measured rather easily at ambient temperature. The spectrum at ambient temperature is used to eliminate background effects from spectra as measured at other surface temperatures. The temperatures of the sample are found in a single calculation from the measured spectra independently of the response function of the instrument and the emissivity of the sample. The spectral emissivity of a sample can be measured if the instrument is calibrated against a blackbody source. Temperatures of blackbody sources are estimated with an uncertainty of 0.2-2 K. The method is demonstrated for measuring the spectral emissivity of a brass specimen and an oxidized nickel specimen.

An experimental investigation is performed to substantiate the capability of a charge coupled device camera to measure local temperature and emissivity of different materials heated to temperatures above 500 °C by two-colour pyrometric technique using colorimetric method. Materials investigated are Inconel 718 with pyromark (high temperature paint), Inconel 718, stainless steel SS 304 and SS 316. Centerline temperature and emissivity distribution is obtained for target plates maintained at constant temperature by AC heating while complete temperature and emissivity distribution is provided for plates heated by flame impingement. The obtained results are compared with a calibrated infrared camera and thermocouples and the temperature distribution is found to be in close agreement. These results pertain to partially oxidized metal alloys covered in this study. Deviation in the measurement of emissivity can be attributed to its dependence on wavelength range, oxidation, and sensitivity of the image detector.

<strong class="journal-contentHeaderColor">Abstract.</strong> Since 2007, the Meteorological Operational satellite (Metop) series of platforms operated by the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) have provided valuable observations of the Earth's surface and atmosphere for meteorological and climate applications. With 15 years of data already collected, the next generation of Metop satellites will see this measurement record extend to and beyond 2045. With a primary role in operational meteorology, tropospheric temperature and water vapour profiles will be key data products produced using infrared and microwave-sounding instruments onboard. Considering the Metop data record that will span 40 years, these profiles will form an essential climate data record (CDR) for studying long-term atmospheric changes. Therefore, the performance of these products must be characterised to support the robustness of any current or future analysis. In this study, we validate 9.5 years of profile data produced using the Infrared and Microwave Sounding (IMS) scheme with the European Space Agency (ESA) Water Vapour Climate Change Initiative (WV_cci) against radiosondes from two different archives. The Global Climate Observing System (GCOS) Reference Upper-Air Network (GRUAN) and Analysed RadioSoundings Archive (ARSA) data records were chosen for the validation exercise to provide the contrast between global observations (ARSA) with sparser characterised climate measurements (GRUAN). Results from this study show that IMS temperature and water vapour profile biases are within 1 K and 10 % of the reference for 'global' scales. We further demonstrate the difference day/night and cloud amount match-ups have on observed biases and discuss the implications sampling also plays on attributing these effects. Finally, we present a first look at the profile bias stability of the IMS product, relating trends in the bias to required climate performance. Overall, we find the results from this study demonstrate the real potential for tropospheric water vapour and temperature profile CDRs from the Metop series of platforms.

A method has been devised for the measurement of spectral and total emissivities of nonmetallic surfaces at high temperatures. The maximum temperature for spectral emissivity measurements is about 1700\ifmmode^\circ\else\textdegree\fi{}C. With an extrapolation of spectral emissivity values it is possible to obtain experimental values for total emissivities at even higher temperatures. This method has been applied in the measurement of the emissivities of polished surfaces of three types of commercially prepared beryllia. Ceramic firing of hot-pressed beryllia was found to have very little, if any, effect on the spectral or total emissivity of a surface formed by polishing the final material. The impurity present in dark samples and/or the larger crystal size increases both the spectral and total emissivity by a factor of about two.

Laboratory calibration and field measurement of land surface temperature and emissivity using thermal infrared multiband radiometers

Combustion properties of pure and fire-retarded cellulose

Water vapour is a crucial and highly variable greenhouse gas in the Earth's atmosphere that plays a major role in the radiative balance, energy transport and photochemical processes. It can also affect the radiative budget indirectly through cloud formation and by altering the size, shape, and chemical composition of aerosol particles. Moreover, monitoring water vapour remains challenging due to its high temporal and spatial variability. Consequently, systematic and accurate observations of water vapour are essential to improve our understanding of its role at both local and global scales and for enhancing climate projections.Advances in remote sensing techniques have enabled continuous acquisition of precipitable water vapour (PWV) measurements using sun/star photometry, microwave radiometry and the Global Navigation Satellite System (GNSS). Nevertheless, none of these instruments provides information on the vertical distribution of water vapour, a critical information considering that water vapour concentrations typically vary by up to three orders of magnitude between the surface and the upper troposphere. In this context, Raman lidar has demonstrated its ability to capture the spatial and temporal evolution of water vapour in the troposphere. Accurate retrievals of the water vapour mixing ratio from Raman lidar measurements rely on robust and well-characterised calibration procedures as well as on an accurate estimation of the differential atmospheric transmission term, which accounts for extinction differences between the molecular reference (nitrogen and oxygen) and water vapour wavelengths.In this study, the lidar calibration constant was determined using a hybrid calibration method, which combines correlative PWV measurements for lidar calibration with Numerical Weather Prediction (NWP) data to reconstruct the water vapour profile within the incomplete overlap region of the lidar system. The differential transmission was estimated using an automated method to account for the aerosol contribution, based on sun photometer Aerosol Optical Depth (AOD) measurements and an exponential decay function with attitude to model aerosol extinction (Díaz-Zurita et al., 2025). Subsequently, a long-term database of water vapour profiles over the period 2009-2022 was generated, providing high vertical and temporal resolution measurements of water vapour over the city of Granada, in Southern Spain. A comprehensive statistical analysis was conducted to characterise the vertical distribution of water vapour over a 14-year period, representing the first long-term vertical characterisation of water vapour in this region. Mean interannual and seasonal water vapour profiles were derived for the entire study period, and trend analyses were performed to assess long-term variations in water vapour content in the lower troposphere. Additionally, lidar-derived PWV values were compared with those obtained from microwave radiometer and GNSS observations.This research was funded by Grant PID2021-128008OB-I00 funded by MICIU/AEI/ 10.13039/501100011033 by ERDF/EU European Union, and by the Spanish national projects CNS2023-145435, PID2023-151817OA-I00 and Marie Skłodowska-Curie Staff Exchange Actions with the project GRASP-SYNERGY (grant agreement no. 10113163). Diaz-Zurita et al. (2025). Remote Sens. 2025, 17(20), 3444; https://doi.org/10.3390/rs17203444

Spaceborne infrared atmospheric sounders measure the spectrum of the upwelling radiance in the infrared with ultra-high spectral resolution. The resolution is sufficient to measure absorption features of atmospheric constituents enabling retrieval of atmospheric temperature and water vapor profiles, surface emission and atmospheric constituents. The Atmospheric Infrared Sounder (AIRS) on Aqua launched in May of 2002 was the first hyperspectral grating-based infrared sounder designed for this purpose and is still operational today. AIRS has been followed by the Infrared Atmospheric Sounding Interferometer (IASI) on MetOp A and B, and the Cross-track Infrared Sounder (CrIS) on Suomi NPP and JPSS. All instruments are operating well improving weather forecast and providing a wealth of information about the atmosphere. Additional CrIS and IASI instruments are expected to be launched providing data of this type into the late 2030’s. AIRS, CrIS and IASI are all Low Earth Orbit (LEO) instruments with nominal spatial resolutions of 14km. Future IR sounders must achieve higher spatial and temporal resolution to match improvements in forecast models and be less costly to match anticipated future budget pressures. Higher temporal resolution can be achieved in several ways including operation in Geostationary Earth Orbit (GEO) or in constellations of LEO satellites. Higher spatial resolution can be achieved using larger format focal plane assemblies in the instruments and larger aperture telescopes. Grating spectrometers are well suited to large format FPAs by allowing a wide field of view in a compact package. They also provide long life and are easy to operate. Concepts for next generation grating spectrometer IR sounders that have been developed over the years at JPL are presented along with technology advancements made to enable these concepts to achieve their stated goals.

Abstract. Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI observations that coincide with Vaisala RS92 radiosonde measurements performed in the framework of the GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) in three different climate zones: the tropics (Manus Island, 2° S), mid-latitudes (Lindenberg, 52° N), and polar regions (Sodankylä, 67° N). The retrievals show good sensitivity with respect to the vertical H2O distribution between 1 km above ground and the upper troposphere. Typical DOFS (degrees of freedom for signal) values are about 5.6 for the tropics, 5.1 for summertime mid-latitudes, 3.8 for wintertime mid-latitudes, and 4.4 for summertime polar regions. The errors of the MUSICA IASI water vapour profiles have been theoretically estimated considering the contribution of many different uncertainty sources. For all three climate regions, unrecognized cirrus clouds and uncertainties in atmospheric temperature have been identified as the most important error sources and they can reach about 25 %. The MUSICA IASI water vapour profiles have been compared to 100 individual coincident GRUAN water vapour profiles. The systematic difference between the data is within 11 % below 12 km altitude; however, at higher altitudes the MUSICA IASI data show a dry bias with respect to the GRUAN data of up to 21 %. The scatter is largest close to the surface (30 %), but never exceeds 21 % above 1 km altitude. The comparison study documents that the MUSICA IASI retrieval processor provides H2O profiles that capture the large variations in H2O volume mixing ratio profiles well from 1 km above ground up to altitudes close to the tropopause. Above 5 km the observed scatter with respect to GRUAN data is in reasonable agreement with the combined MUSICA IASI and GRUAN random errors. The increased scatter at lower altitudes might be explained by surface emissivity uncertainties at the summertime continental sites of Lindenberg and Sodankylä, and the upper tropospheric dry bias might suggest deficits in correctly modelling the spectroscopic line shapes of water vapour.

Efficient use of water in agro-ecosystems requires accurate quantification of actual evapotranspiration (ETa). The two-step approach, i.e., reference ET (ETref) adjusted with crop coefficients (Kc), is an extensively used approach to estimate ETa. Explicit combination equations, i.e., Penman-type combination-based equations and their derivatives (e.g., Penman-Monteith, ASCE-EWRI Penman-Monteith), have been widely tested and used. These equations rely on an assumption to remove the surface temperature from the calculation, and the validity of this assumption has been questioned as likely underestimating ET, particularly in semiarid and arid climates. Information on the validity of this assumption in subhumid regions is rare. Recursive combination methods, based on an equation proposed by Budyko, make no assumptions for the surface temperature, but they require iteration to arrive at a solution. The objective of this research was to compare ET calculated by explicit and recursive combination equations with measured values from a Bowen ratio energy balance system (BREBS) for an irrigated grassland. Results indicated that both equations were very sensitive to the value used for the surface resistance (rs). For equivalent values of rs, the explicit and recursive combination equations performed nearly equally as well in predicting BREBS-measured ET on both hourly and daily time steps. A surface resistance value of 40 s m-1 provided the best fit between both the Budyko and ASCE-EWRI equation-estimated ET and the measured ET values. Root mean square difference (RMSD) using rs = 40 s m-1 was 0.06 mm h-1, and model efficiency and R2 were both greater than 0.90. The same value (rs = 40 s m-1) also provided the best fit for nighttime ET estimates. Similarly, a daytime rs of 40 s m-1 provided the best fit between the ASCE-EWRI equation estimate and measured ET. On a daily time step, a sum-of-hourly approach provided better agreements with the BREBS-measured ET for both explicit (R2 = 0.95, RMSD = 0.57 mm d-1) and recursive (R2 = 0.96, RMSD = 0.57 mm d-1) combination methods than calculating ET using a daily average approach (explicit: R2 = 0.82, RMSD = 0.64 mm d-1; recursive: R2 = 0.78, RMSD = 0.72 mm d-1). While the recursive combination equation may potentially provide more accuracy under some conditions (i.e., arid and semiarid regions), it was no more accurate than the explicit equation under these experimental conditions.

The accuracy of brightness temperature (BT) from the Cross-track Infrared Sounder (CrIS) onboard the Suomi National Polar-orbiting Partnership (S-NPP) satellite and NOAA-20 is estimated using the Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) radio occultation (RO) wet retrievals (temperature and water vapor profiles) as input to the Community Radiative Transfer Model (CRTM). The matchup criteria between RO and CrIS observations are time less than 30 min, a distance less than 50 km, and over oceans to reduce the collocation and simulation uncertainty. Based on the information provided in the CrIS and RO observations, only upper temperature sounding channels with weighting function peak height (WFPH) above 200 hPa (~12 km) from the CrIS longwave infrared (LWIR) and shortwave infrared (SWIR) bands and water vapor channels from the CrIS mid-wave infrared (MWIR) band with WFPH above 500 hPa (~6.3 km) are selected for comparison to minimize the impacts from the surface emission, cloud absorption/scattering, and atmospheric gaseous absorption. The absolute differences between CrIS observations and their CRTM simulations using RO data as input are less than 1.0 K for the majority of those selected channels. The double differences between CrIS observations on NOAA-20 and S-NPP using CRTM simulations as transfer references are very stable. They range from −0.05 K to 0.15 K for LWIR channels and −0.20 K to 0.10 K for SWIR channels during the two years from 1 October 2019 to 30 September 2021. For MWIR channels, the double differences range from −0.15 K to 0.25 K but have significant variations in both daily mean and monthly mean time series. The results provide ways to understand the qualities of RO retrieval and CrIS measurements: RO data can be used to assess the consistency and stability of CrIS observations quantitatively, and CrIS measurements have the quality to assess the quality and stability of RO retrievals.