Comparison of modeled and empirical approaches for retrieving columnar water vapor from solar transmittance measurements in the 0.94 micrometer region

Four atmospheric transmittance models, LOWTRAN 7, MODTRAN 3, FASCOD3P, and the Thomason model, are investigated to quantify the relationship between water vapor transmittance as function of water vapor amount, Tw (U), for an instrument specific band pass in the 0.94-um region. In a second step an empirical Tw (U) function is established using long term measurements with our high-precision Sun photometer (SPM) in Bern, Switzerland along with 1300 simultaneous and collocated water vapor retrievals performed with a dual-channel microwave radiometer (MWR). In order to avoid a possible bias in the empirical Tw(U) function, the MWR data set is prescreened by comparing retrievals coincident with radiosonde ascents. Over a 2 1/2-year period of common observations, radiosondes and PM agreed to within 0.19 cm (13%) of columnar water vapor (CWV) using the empirical Tw (U) relationship. Completely independent comparisons with an additional MWR and two Fourier transform spectrometers yielded agreement within 13% and 9%, respectively. Comparing empirical and modeled results, we found that with respect to the experimental data, LOWTRAN 7, MODTRAN 3, and FASCOD3P reported higher water vapor transmittances over almost the entire range of realistic absorber amounts. By relating these differences to differences in retrieved CWV for the case of two standard atmospheres, we found that using Tw (U) predicted by LOWTRAN 7, MODTRAN 3, and FASCOD3P leads to an overestimate of CWV by about 18-30%, 7-20%, and 2-18%, respectively. The Thomason model yields good agreement with respect to the experimental data up to medium absorber amounts, whereas at slant path amounts larger than 10 cm, errors up to 60% in retrieved CWV occurred. We also show in this work that a misinterpretation of the LOWTRAN 7 water vapor output counterbalances incorrectly predicted Tw, leading to results that agree well with experimental one

Heat Transfer and Pressure Drop of R1123/R32 (40/60 mass%) Flow in Horizontal Microfin Tubes during Condensation and Evaporation

In this study, the heat transfer coefficient (HTC) and pressure drop of the new low global warming potential refrigerant mixture R1123/R32 (40/60 mass%) in a 6.0 mm OD horizontal microfin tube during condensation at 40 °C and evaporation at 10 °C are experimentally quantified. The data are then compared to the component R32. Both the condensation HTC and pressure drop of R1123/R32 (40/60 mass%) are somewhat lower than those of R32. Similarly, the pressure drop of R1123/R32 during the evaporation process at 10 °C is somewhat lower than that of R32. However, the evaporation HTC is comparable to that of R32. The lower surface tension of R1123/R32 can enhance the nucleate boiling and compensate the heat transfer degradation due to the volatility difference

Intercomparison of Landsat OLI and Terra ASTER solar reflective calibrations using the Radiometric Calibration Network data from Railroad Valley, Nevada

This paper presents an intercomparison study between the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Landsat 8 Operational Land Imager (OLI) using data from the Radiometric Calibration Network (RadCalNet). The study evaluates the radiometric performance and agreement between ASTER and Landsat 8 OLI, focusing on their spectral bands relevant for vegetation analysis and land cover classification. The analysis includes the assessment of data quality, uncertainties, and factors influencing the measurements. The results demonstrate the usability of RadCalNet in evaluating the accuracy and reliability of remote sensing data. The findings contribute to our understanding of the strengths and limitations of ASTER and Landsat 8 OLI, supporting informed decision-making in environmental monitoring and resource management. Overall, the intercomparison study provides valuable insights into the capabilities and limitations of ASTER and Landsat 8 OLI, highlighting the importance of RadCalNet in assessing the radiometric performance of remote sensing sensors. The results from the Railroad Valley RadCalNet show that the site is suitable for sensors with spatial resolutions as small as 15 m. The comparison between ASTER and OLI demonstrates that the recent update to the ASTER radiometric calibration provides results that are in agreement with Landsat 8 OLI to well within the absolute radiometric uncertainties of both sensors. © 2023 SPIE · 0277-786X.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Traceable radiometry underpinning terrestrial- and helio-studies (TRUTHS)

The Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) mission offers a novel approach to the provision of key scientific data with unprecedented radiometric accuracy for Earth Observation (EO) and solar studies, which will also establish well-calibrated reference targets/standards to support other EO missions. This paper presents the TRUTHS mission and its objectives. TRUTHS will be the first satellite mission to calibrate its EO instrumentation directly to SI in orbit, overcoming the usual uncertainties associated with drifts of sensor gain and spectral shape by using an electrical rather than an optical standard as the basis of its calibration. The range of instruments flown as part of the payload will also provide accurate input data to improve atmospheric radiative transfer codes by anchoring boundary conditions, through simultaneous measurements of aerosols, particulates and radiances at various heights. Therefore, TRUTHS will significantly improve the performance and accuracy of EO missions with broad global or operational aims, as well as more dedicated missions. The provision of reference standards will also improve synergy between missions by reducing errors due to different calibration biases and offer cost reductions for future missions by reducing the demands for on-board calibration systems. Such improvements are important for the future success of strategies such as Global Monitoring for Environment and Security (GMES) and the implementation and monitoring of international treaties such as the Kyoto Protocol. TRUTHS will achieve these aims by measuring the geophysical variables of solar and lunar irradiance, together with both polarised and unpolarised spectral radiance of the Moon, Earth and its atmosphere. Published by Elsevier Ltd on behalf of COSPAR