Inflight performance of the state-of-the-art BepiColombo MORE radio-tracking system 

2021 ◽  
Author(s):  
Paolo Cappuccio ◽  
Luciano Iess ◽  
Daniele Durante ◽  
Ivan di Stefano ◽  
Paolo Racioppa ◽  
...  
Keyword(s):  
Water Vapor ◽  
Tracking System ◽  
Weather Conditions ◽  
Integration Time ◽  
Path Delay ◽  
Noise Component ◽  
Ka Band ◽  
Range Measurements ◽  
Radio Science ◽  
Range Rate

<p>The ESA/JAXA mission BepiColombo, launched on 20 October 2018 is in cruise towards Mercury and will arrive at Mercury in 2025 to investigate its surface, interior structure and magnetosphere. The Mercury Orbiter Radio-science Experiment (MORE) onboard the Mercury Planetary Orbiter (MPO) aims at determining the gravity field, the rotational state and librations of the planet, using precise tracking of the spacecraft during its orbital phase around Mercury. Range and range-rate measurements collected during the cruise phase will be used to test the theory of general relativity starting in March 2021. The MORE experiment exploits two-way multifrequency microwave links from ESA and NASA: two downlinks in X- and Ka-band coherent with the X-band uplink and one Ka-band downlink coherent with the Ka-band uplink. The range-rate and range measurements accurately BepiColombo’s line-of-sight velocity and the round-trip light-time of the signal, respectively. The calibration of the dispersive plasma noise component through the combination of the X/X, X/Ka and Ka/Ka links and the use of water vapor radiometers to correct for the path delay due to Earth’s troposphere will result in an accuracy of ~3 µm/sec (at 1000-s integration time) on the Doppler and centimeter-level range accuracies. We report on the analysis of dedicated tests executed on range and Doppler data collected by ESA and NASA stations at X and Ka-band. The comparison of the observed noise with the predictions shows results exceeding the expectations. In particular, the 24 Mcps pseudo-noise modulation of the Ka-band carrier, enabled by MORE’s KaT transponder built by Thales Alenia Space Italia, provided two-way range measurements accurate to ~3 cm with just 4 s integration time, at a distance of 0.7 AU, September 2021, and 1.3 AU, November 2021. Under favorable weather conditions, the range rate has shown an accuracy of 25 µm/s at 10 s integration time, in line with the expected end-to-end performance. Under unfavorable weather conditions the performance was slightly over the requirements. We must remark that calibrations from water vapor radiometers were not available during these tests and only GNSS calibration were applied.</p>

scholarly journals VESPA-22: a ground-based microwave spectrometer for long-term measurements of Polar stratospheric water vapor

2017 ◽  
Author(s):  
Gabriele Mevi ◽  
Giovanni Muscari ◽  
Pietro Paolo Bertagnolio ◽  
Irene Fiorucci ◽  
Giandomenico Pace
Keyword(s):  
Water Vapor ◽  
Weather Conditions ◽  
Black Body ◽  
High Arctic ◽  
Frequency Resolution ◽  
Integration Time ◽  
Vertical Profiles ◽  
Stratospheric Water Vapor ◽  
Sensitivity Range ◽  
Half Power

Abstract. The new ground-based 22 GHz spectrometer, VESPA-22 (water Vapor Emission Spectrometer for Polar Atmosphere at 22 GHz) measures the 22.23 GHz water vapor emission line with a bandwith of 500 MHz and a frequency resolution of 31 kHz. The integration time for a measurement is of the order of hours, depending on season and weather conditions. Water vapor spectra are collected using the beam switching technique. VESPA-22 is designed to operate automatically with minimum need of maintenance; it employs an uncooled front-end characterized by a receiver temperature of about 180 K and its quasi-optical system presents a half power full beam angle of 3.5°. VESPA-22 measures also the sky opacity with a temporal resolution of two measurements an hour using the tipping curve technique. The instrument calibration is performed automatically by a noise diode; the emission temperature of this element is measured two times an hour through the observation of a black body at ambient temperature and of the sky at 60° of elevation. The retrieved profiles obtained inverting a 24-hour integration spectra present a sensitivity higher than 0.8 from about 25 to 72 km of altitude, a vertical resolution from about 12 to 23 km (depending on altitude) and an overall 1σ uncertainty between 5 and 12 %. In July 2016, VESPA-22 was installed at the THAAO (Thule High Arctic Atmospheric Observatory) located at Thule Air Base (76.5° N, 68.8° W), Greenland, and has been operating almost continuously since then, with very few interruption periods characterized by poor weather. The VESPA-22 water vapor mixing ratio vertical profiles discussed in this work cover the period from July 2016 to May 2017 and are compared with Version 4.2 of concurrent Aura/MLS (Waters et al., 2006) water vapor vertical profiles. In the sensitivity range of VESPA-22 retrievals, the intercomparison between the VESPA-22 dataset and Aura/MLS dataset convolved with VESPA-22 averaging kernels reveals a correlation coefficient of about 0.9 or higher and an average difference reaching its maximum of −6 % or −0.2 ppmv at the top of the sensitivity range.

scholarly journals VESPA-22: a ground-based microwave spectrometer for long-term measurements of polar stratospheric water vapor

2018 ◽  
Vol 11 (2) ◽  
pp. 1099-1117 ◽  
Author(s):  
Gabriele Mevi ◽  
Giovanni Muscari ◽  
Pietro Paolo Bertagnolio ◽  
Irene Fiorucci ◽  
Giandomenico Pace
Keyword(s):  
Water Vapor ◽  
Weather Conditions ◽  
Black Body ◽  
High Arctic ◽  
Frequency Resolution ◽  
Integration Time ◽  
Vertical Profiles ◽  
Stratospheric Water Vapor ◽  
Water Vapor Mixing Ratio ◽  
Beam Switching

Abstract. The new ground-based 22 GHz spectrometer, VESPA-22 (water Vapor Emission Spectrometer for Polar Atmosphere at 22 GHz) measures the 22.23 GHz water vapor emission line with a bandwidth of 500 MHz and a frequency resolution of 31 kHz. The integration time for a measurement ranges from 6 to 24 h, depending on season and weather conditions. Water vapor spectra are collected using the beam-switching technique. VESPA-22 is designed to operate automatically with little maintenance; it employs an uncooled front-end characterized by a receiver temperature of about 180 K and its quasi-optical system presents a full width at half maximum of 3.5∘. Every 30 min VESPA-22 measures also the sky opacity using the tipping curve technique. The instrument calibration is performed automatically by a noise diode; the emission temperature of this element is estimated twice an hour by observing alternatively a black body at ambient temperature and the sky at an elevation of 60∘. The retrieved profiles obtained inverting 24 h integration spectra present a sensitivity larger than 0.8 from about 25 to 75 km of altitude during winter and from about 30 to 65 km during summer, a vertical resolution from about 12 to 23 km (depending on altitude), and an overall 1σ uncertainty lower than 7 % up to 60 km altitude and rapidly increasing to 20 % at 75 km. In July 2016, VESPA-22 was installed at the Thule High Arctic Atmospheric Observatory located at Thule Air Base (76.5∘ N, 68.8∘ W), Greenland, and it has been operating almost continuously since then. The VESPA-22 water vapor mixing ratio vertical profiles discussed in this work are obtained from 24 h averaged spectra and are compared with version 4.2 of concurrent Aura/Microwave Limb Sounder (MLS) water vapor vertical profiles. In the sensitivity range of VESPA-22 retrievals, the intercomparison from July 2016 to July 2017 between VESPA-22 dataset and Aura/MLS dataset convolved with VESPA-22 averaging kernels shows an average difference within 1.4 % up to 60 km altitude and increasing to about 6 % (0.2 ppmv) at 72 km.

scholarly journals Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference

2020 ◽  
Vol 12 (7) ◽  
pp. 1170 ◽  
Author(s):  
Cintia Carbajal Henken ◽  
Lisa Dirks ◽  
Sandra Steinke ◽  
Hannes Diedrich ◽  
Thomas August ◽  
...  
Keyword(s):  
Water Vapor ◽  
Pairwise Comparison ◽  
Weather Conditions ◽  
Satellite System ◽  
High Temporal Resolution ◽  
Data Sets ◽  
Frequency Distributions ◽  
Temporal Sampling ◽  
Global Navigation Satellite ◽  
Satellite Instruments

Passive imagers on polar-orbiting satellites provide long-term, accurate integrated water vapor (IWV) data sets. However, these climatologies are affected by sampling biases. In Germany, a dense Global Navigation Satellite System network provides accurate IWV measurements not limited by weather conditions and with high temporal resolution. Therefore, they serve as a reference to assess the quality and sampling issues of IWV products from multiple satellite instruments that show different orbital and instrument characteristics. A direct pairwise comparison between one year of IWV data from GPS and satellite instruments reveals overall biases (in kg/m 2 ) of 1.77, 1.36, 1.11, and −0.31 for IASI, MIRS, MODIS, and MODIS-FUB, respectively. Computed monthly means show similar behaviors. No significant impact of averaging time and the low temporal sampling on aggregated satellite IWV data is found, mostly related to the noisy weather conditions in the German domain. In combination with SEVIRI cloud coverage, a change of shape of IWV frequency distributions towards a bi-modal distribution and loss of high IWV values are observed when limiting cases to daytime and clear sky. Overall, sampling affects mean IWV values only marginally, which are rather dominated by the overall retrieval bias, but can lead to significant changes in IWV frequency distributions.

scholarly journals Spectrally-Resolved Raman Lidar to Measure Atmospheric Three-Phase Water Simultaneously

2020 ◽  
Vol 237 ◽  
pp. 06017
Author(s):  
Fuchao Liu ◽  
Fan Yi
Keyword(s):  
Water Vapor ◽  
Raman Spectra ◽  
Weather Conditions ◽  
Cloud Microphysics ◽  
Raman Lidar ◽  
Atmospheric Water ◽  
Three Phase ◽  
Phase Water ◽  
Spectrally Resolved ◽  
Ice Water

We report on a spectrally-resolved Raman lidar that can simultaneously profile backscattered Raman spectrum signals from water vapor, water droplets and ice crystals as well as aerosol fluorescence in the atmosphere. The lidar emits a 354.8-nm ultraviolet laser radiation and samples echo signals in the 393.0-424.0 nm wavelength range with a 1.0-nm spectral resolution. A spectra decomposition method is developed to retrieve fluorescence spectra, water vapor Raman spectra and condensed (liquid and/or ice) water Raman spectra successively. Based on 8 different clear-sky nighttime measurement results, the entire atmospheric water vapor Raman spectra are for the first time obtained by lidar. The measured normalized water vapor Raman spectra are nearly invariant and can serve as background reference for atmospheric water phase state identification under various weather conditions. For an ice virga event, it’s found the extracted condensed water Raman spectra are highly similar in shape to theoretical ice water Raman spectra reported by Slusher and Derr (1975). In conclusion, the lidar provides an effective way to measure three-phase water simultaneously in the atmosphere and to study of cloud microphysics as well as interaction between aerosols and clouds.

scholarly journals Dual Axis Solar Tracker with Weather Sensor

2019 ◽  
Vol 8 (2S11) ◽  
pp. 3308-3311
Keyword(s):  
Energy Conversion ◽  
Tracking System ◽  
Weather Conditions ◽  
Maximum Amount ◽  
Control Element ◽  
Sensing Element ◽  
Advanced Level ◽  
Solar Tracking ◽  
Solar Tracker ◽  
Arduino Uno

This paper presents the outline and execution of simple, easy and cheaper automatic dual axis solar tracking system using Arduino UNO as the control element and light detecting sensors (LDRS) as the sensing element. This project involves advanced level of technology to capture maximum amount of energy using sun’s radiations. The main purpose is to increase the efficiency of tracking system which can rotate in all four directions continuously according to intensity of radiations and for energy conversion. In this, the voltage from panel is calculated from time to time in an interval of 1hr and this voltage is used to sense the weather conditions and display the climatic temperatures

scholarly journals The Impacts of Tracking System Inaccuracy on CPV Module Power

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1278
Author(s):  
Henrik Zsiborács ◽  
Nóra Baranyai ◽  
András Vincze ◽  
Philipp Weihs ◽  
Stefan Schreier ◽  
...  
Keyword(s):  
Tracking System ◽  
Tracking Error ◽  
Weather Conditions ◽  
Cell Diameter ◽  
Tracking Accuracy ◽  
Optimal Position ◽  
Climate Conditions ◽  
Solar Tracking ◽  
Power Yield ◽  
The Difference

The accuracy and reliability of solar tracking greatly impacts the performance of concentrator photovoltaic modules (CPV). Thus, it is of utmost significance to know how deviations in tracking influence CPV module power. In this work, the positioning characteristics of CPV modules compared to the focus points were investigated. The performance of CPV modules mounted on a dual-axis tracking system was analysed as a function of their orientation and inclination. The actual experiment was carried out with CPV cells of 3 mm in diameter. By using a dual tracking system under real weather conditions, the module’s position was gradually modified until the inclination differed by 5° relative to the optimal position of the focus point of the CPV module. The difference in inclination was established by the perfect perpendicularity to the Sun’s rays. The results obtained specifically for CPV technology help determine the level of accuracy that solar tracking photovoltaic systems are required to have to keep the loss in power yield under a certain level. Moreover, this power yield loss also demonstrated that the performance insensitivity thresholds of the CPV modules did not depend on the directions of the alterations in azimuthal alignment. The novelty of the research lies in the fact that earlier, no information had been found regarding the tracking insensitivity point in CPV technologies. A further analysis was carried out to compare the yield of CPV to other, conventional photovoltaic technologies under real Central European climate conditions. It was shown that CPV needs a sun tracking accuracy of at least 0.5° in order to surpass the yield of other PV technologies. Besides providing an insight into the tracking error values of solar tracking sensors, it is believed that the results might facilitate the planning of solar tracking sensor investments as well as the economic calculations related to 3 mm cell diameter CPV system investments.

scholarly journals Assessments of GMI-Derived Precipitable Water Vapor Products over the South and East China Seas Using Radiosonde and GNSS

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
Biyan Chen ◽  
Wujiao Dai ◽  
Zhizhao Liu ◽  
Lixin Wu ◽  
Pengfei Xia
Keyword(s):  
Water Vapor ◽  
Weather Forecasting ◽  
Microwave Radiometer ◽  
Precipitable Water ◽  
Weather Conditions ◽  
Precipitable Water Vapor ◽  
East China ◽  
China Seas ◽  
The South ◽  
Mean Square Errors

Satellite remote sensing of the atmospheric water vapor distribution over the oceans is essential for both weather and climate studies. Satellite onboard microwave radiometer is capable of measuring the water vapor over the oceans under all weather conditions. This study assessed the accuracies of precipitable water vapor (PWV) products over the south and east China seas derived from the Global Precipitation Measurement Microwave Imager (GMI), using radiosonde and GNSS (Global Navigation Satellite System) located at islands and coasts as truth. PWV measurements from 14 radiosonde and 5 GNSS stations over the period of 2014–2017 were included in the assessments. Results show that the GMI 3-day composites have an accuracy of better than 5 mm. A further evaluation shows that RMS (root mean square) errors of the GMI 3-day composites vary greatly in the range of 3∼14 mm at different radiosonde/GNSS sites. GMI 3-day composites show very good agreements with radiosonde and GNSS measured PWVs with correlation coefficients of 0.896 and 0.970, respectively. The application of GMI products demonstrates that it is possible to reveal the weather front, moisture advection, transportation, and convergence during the Meiyu rainfall. This work indicates that the GMI PWV products can contribute to various studies such as climate change, hydrologic cycle, and weather forecasting.

scholarly journals Optimized Single-Axis Schedule Solar Tracker in Different Weather Conditions

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5226
Author(s):  
Nurzhigit Kuttybay ◽  
Ahmet Saymbetov ◽  
Saad Mekhilef ◽  
Madiyar Nurgaliyev ◽  
Didar Tukymbekov ◽  
...  
Keyword(s):  
Rotation Angle ◽  
Tracking System ◽  
Weather Conditions ◽  
Main Task ◽  
Solar Panels ◽  
Simple Method ◽  
Solar Tracking ◽  
Rainy Weather ◽  
Solar Tracker ◽  
One Year

Improving the efficiency of solar panels is the main task of solar energy generation. One of the methods is a solar tracking system. One of the most important parameters of tracking systems is a precise orientation to the Sun. In this paper, the performance of single-axis solar trackers based on schedule and light dependent resistor (LDR) photosensors, as well as a stationary photovoltaic installation in various weather conditions, were compared. A comparative analysis of the operation of a manufactured schedule solar tracker and an LDR solar tracker in different weather conditions was performed; in addition, a simple method for determining the rotation angle of a solar tracker based on the encoder was proposed. Finally, the performance of the manufactured solar trackers was calculated, taking into account various weather conditions for one year. The proposed single-axis solar tracker based on schedule showed better results in cloudy and rainy weather conditions. The obtained results can be used for designing solar trackers in areas with a variable climate.

Seven-Point Solar Tracking Control for a Fiber-Optic Daylighting System

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Rahate Ahmed ◽  
Yeongmin Kim ◽  
Zeeshan ◽  
Muhammad Uzair Mehmood ◽  
Hyun Joo Han ◽  
...  
Keyword(s):  
Tracking Control ◽  
Tracking System ◽  
Weather Conditions ◽  
Fresnel Lens ◽  
Solar Tracking ◽  
Stepper Motors ◽  
Solar Tracker ◽  
Series Of Experiments ◽  
Optical Fiber Cable ◽  
Cloud Effect

Abstract A strategy for precise solar tracking has been developed using feedback signals from seven photosensors in conjunction with the operation of an active daylighting system. The tracking system was composed of a microcontroller, two stepper motors, photosensors, a grooves-in Fresnel lens concentrator, and a glass optical fiber cable. A robust control was implemented using cadmium sulfide (CdS) sensors to track the sun’s path precisely from sunrise to sunset. To avoid the cloud effect, two separate sensors were installed apart from the main tracking sensors. The control system was allowed to track the sun’s position if clouds covered the sky continuously for less than approximately 70 min. To analyze the performance of the solar tracker for daylighting applications, a series of experiments were performed in different weather conditions where the accuracy and effectiveness of the present solar tracking control were confirmed.

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