Low Elevation Angles Research Articles

Analysis of Illumination Conditions in the Lunar South Polar Region Using Multi-Temporal High-Resolution Orbital Images

The illumination conditions of the lunar south pole region are complex due to the rugged terrain and very low solar elevation angles, posing significant challenges to the safety of lunar landing and rover explorations. High-spatial and temporal-resolution analyses of the illumination conditions in the south pole region are essential to support mission planning and surface operations. This paper proposes a method for illumination condition analysis in the lunar pole region using multi-temporal high-resolution orbital images with a pre-selected landing area of Chang’E-7 as the study area. Firstly, a database of historical multi-temporal high-resolution (0.69–1.97 m/pixel) orbital images, with associated image acquisition time, solar elevation angle, and azimuth angle, is established after preprocessing and registration. Secondly, images with the nearest solar elevation and azimuth at the planned time for mission operations are retrieved from the database for subsequent illumination condition analysis and exploration support. The differences in the actual solar positions at the mission moments from that of the nearest sun position image are calculated and their impact on illumination conditions is evaluated. Experimental results of the study area demonstrate that the constructed image database and the proposed illumination analysis method using multi-temporal images, with the assistance of DEM in a small number of cases, can effectively support the mission planning and operations for the Chang’E-7 mission in the near future.

Satellite-based assessment of national carbon monoxide concentrations for air quality reporting in Finland

Carbon monoxide (CO) has negative health effects, especially on the respiratory system, when present in large concentrations in ambient air. Therefore, it is one of the 12 air pollutants with monitoring and assessment obligations set by the European Union Ambient Air Quality Directives. With low CO concentrations in Finland, continuous surface measurements are not compulsory but the monitoring and assessment obligation remains. Currently, there are no air quality stations equipped with CO measurements in Finland, and the assessment can only be based on emission estimates.In this work, we demonstrate the use of satellite-based CO measurements from the TROPOspheric Monitoring Instrument (TROPOMI) on-board Sentinel-5 Precursor satellite (S5P) to strengthen the assessment with actual measurements. Averaging satellite measurements over several years reveals the spatial distribution of CO with nationwide coverage in city-scale resolution. Individual satellite measurements, in turn, are used to estimate the surface concentrations and their annual variability in different regions in Finland.For the surface estimates, we used a simple and robust linear model between the satellite measurements and ground-level in-situ measurements. We found that the linear model produces reasonable surface concentration estimates to be used in air quality assessments where the objective is to evaluate whether the monitoring threshold set by the EU is exceeded on a yearly scale. It is noted that cloudiness can cause local data gaps of several days and the low solar elevation angles prevent satellite measurements from 9 to 18 weeks during the winter time in Finland.In Finland, the average total columns show low spatial variability, with only a few high-concentration areas identified. For the last three years, the estimated surface concentrations have stayed well below the lower assessment threshold set by the Air Quality Directive.

Satellite to buoy IoT communications in the Arctic Ocean

Internet of things (IoT), to Arctic Ocean areas using Low Earth Orbit (LEO) satellites for communication to and from sensor units on the sea, has become increasingly important. It is challenging to close the link budget from a buoy on sea to a LEO satellite due to restrictions on the availability of power in such installations. Phenomena as scattering from the sea surface and small-scale fading, ionospheric scintillations, diffraction loss at low elevation angles, and power availability in small LEO satellites and models for analysis are described. It is of great importance to have a radio wave propagation model that accurately predicts path loss between an installation on the sea and a LEO satellite taking all loss mechanisms into account. In this paper, a path-loss model for satellite to buoy communications over the sea is described. In this model, maritime propagation phenomena in the radio link include free space loss, scintillation loss caused by the ionosphere, diffraction loss at low elevation angle, and scattering at the sea surface depending on the wave height and small-scale fading. Furthermore, a buoy on the sea surface with strong angular movement will cause a varying receive signal level depending on the antenna diagram. These phenomena are assessed. A link budget for the frequencies 433, 868, and 3,400 MHz is calculated for a LEO satellite at a height of 800 km.

An Improved Carrier-Smoothing Code Algorithm for BDS Satellites with SICB

Carrier Smoothing Code (CSC), as a low-pass filter, has been widely used in GNSS positioning processing to reduce pseudorange noise via carrier phases. However, current CSC methods do not consider the systematic bias between the code and carrier phase observation, also known as Satellite-induced Code Bias (SICB). SICB has been identified in the BDS-2 and the bias will reduce the accuracy or reliability of the CSC. To confront bias, an improved CSC algorithm is proposed by considering SICB for GEO, IGSO, and MEO satellites in BDS constellations. The correction model of SICB for IGSO/MEO satellites is established by using a 0.1-degree interval piecewise weighted least squares Third-order Curve Fitting Method (TOCFM). The Variational Mode Decomposition combined with Wavelet Transform (VMD-WT) is proposed to establish the correction model of SICB for the GEO satellite. To verify the proposed method, the SICB model was established by collecting 30 Multi-GNSS Experiment (MGEX) BDS stations in different seasons of a year, in which the BDS data of ALIC, KRGG, KOUR, GCGO, GAMG, and SGOC stations were selected for 11 consecutive days to verify the effectiveness of the algorithm. The results show that there is obvious SICB in the BDS-2 Multipath (MP) combination, but the SICB in the BDS-3 MP is smaller and can be ignored. Compared with the modeling in the references, TOCFM is more suitable for IGSO/MEO SICB modeling, especially for the SICB correction at low elevation angles. After the VMD-WT correction, the Root Mean Square Error (RMSE) of SICB of B1I, B2I, and B3I in GEO satellites is reduced by 53.35%, 63.50%, and 64.71% respectively. Moreover, we carried out ionosphere-free Single Point Positioning (IF SPP), Ionosphere-free CSC SPP (IF CSC SPP), CSC single point positioning with the IGSO/MEO SICB Correction based on the TOCFA Method (IGSO/MEO SICB CSC), and CSC single point positioning with the IGSO/MEO/GEO SICB correction based on VMD-WT and TOCFA (IGSO/MEO/GEO SICB CSC), respectively. Compared to IF SPP, the average improvement of the IGSO/MEO/GEO SICB CSC algorithm in the north, east, and up directions was 24.42%, 27.94%, and 24.98%, respectively, and the average reduction in 3D RMSE is 24.54%. Compared with IF CSC SPP, the average improvement of IGSO/MEO/GEO SICB CSC is 7.03%, 6.50%, and 10.48% in the north, east, and up directions, respectively, while the average reduction in 3D RMSE was 9.86%. IGSO/MEO SICB mainly improves the U direction positioning accuracy, and GEO SICB mainly improves the E and U direction positioning accuracy. After the IGSO/MEO/GEO SICB correction, the overall improvement was about 10% and positioning improved to a certain extent.

Reliability and Concurrent Validity of Smartphone Clinometer Application for Measuring Scapular Rotations in Subjects With and Without Shoulder Pain.

Clinical assessment of scapular motion is obscured by a lack of clinically accessible and feasible angular measurement tools. This study evaluates the reliability and validity of the smartphone "Clinometer" app in measuring scapular upward rotation (UR) and anteroposterior tilt. Psychometric analysis. We recruited 57 participants-10 with and 47 without shoulder pain. Two physical therapists consecutively measured both scapular movements using the Clinometer app at the arm by the side (rest), 30°, 60°, 90°, and 120° of humeral elevation in the scapular plane; one therapist measured again after 2days. For evaluating concurrent validity, we compared the Clinometer scores with those measured using an electromagnetic motion capture system in 10 healthy participants. Intraclass correlation coefficients (ICC) with standard error of measurement (SEM) and minimal detectable difference at 90% confidence intervals (MDD90) were calculated. Concurrent validity was evaluated using repeated-measures analysis of variance followed by post hoc testing with Tukey-Kramer test (P < .05). We observed good intrarater reliability (ICC: UR = .76-.85, tilt = .69-.9; SEM: 2.2°-3.5°; MDD90: ∼5°-8°) and moderate to good interrater reliability (ICC: UR = .66-.78, tilt = .66-.76; SEM: 3.6°-8°; MDD90: ∼9°-18°) for both rotations. The Clinometer scores for UR were comparable to electromagnetic motion capture system at all angles except 90° (difference ∼8°); for scapular tilt, the scores were comparable only at rest and 30° elevation. The Clinometer app is reliable and valid for measuring scapular UR throughout and for scapular tilt at lower humeral elevation angles. The MDD90 values for scapular rotations computed in this study can be helpful in rehabilitation planning and future research.

A Low-Cost High-Throughput C-Band Communication System for CubeSats

This paper presents the physical layer of a proprietary broadband communication system for CubeSats. The system operates in the C band (5.8 GHz), delivering at least 10 Mbps of the net user throughput. Operation at low elevation angles (and therefore low SNRs) and high Doppler shifts is made possible thanks to a sophisticated synchronization subsystem. The system can be adapted to propagation conditions experienced during a given visibility window by changing the signal bandwidth and coding rate. It is implemented using Software Defined Radio (SDR) technology. The system will be used in two missions that are scheduled for 2023 and 2024 and are planned in cooperation with the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” and SatRev S.A.

ROTI and scintillation index correlation under quiet and disturbed periods over an Indian low latitude station, Waltair

The variation of correlation between ROTI and S4 index is examined by using GPS L1 and L5 signals over an Indian low latitude station, Waltair (17.73° N, 83.37° E) during the period from 2015 to 2017. The effect of geomagnetic storms on the correlation between ROTI and S4 index is the main focus of the present study. The influence of satellite elevation angle and signal frequency on the correlation between ROTI and S4 index is also investigated during different seasons and geomagnetic conditions. The correlation is found to vary between 0.28 and 0.63 for elevation angles above 30⁰ and between 0.56 and 0.87 for the elevation angles above 50⁰. The correlation coefficient values are decreasing with solar activity from 2015 to 2017 during quiet and disturbed geomagnetic periods. From the analysis on the seasonal correlation between ROTI and S4 index, it is found that solar activity dependent seasonal correlation is observed for both GPS L1 and L5 signals over lower elevation angle 30⁰. The correlation between ROTI and S4 index is increasing over higher elevation angles and for lower signal frequency.

The Baryonic Content of Galaxies Mapped by MaNGA and the Gas Around Them

We analyze the cool gas in and around 14 nearby galaxies (at z < 0.1) mapped with the Sloan Digital Sky Survey IV MaNGA survey by measuring absorption lines produced by gas in spectra of background quasars/active galactic nuclei at impact parameters of 0–25 effective radii from the galactic centers. Using Hubble Space Telescope/Cosmic Origins Spectrograph, we detect absorption at the galactic redshift and measure or constrain column densities of neutral (H i, N i, O i, and Ar i), low-ionization (Si ii, S ii, C ii, N ii, and Fe ii), and high-ionization (Si iii, Fe iii, N v, and O vi) species for 11 galaxies. We derive the ionization parameter and ionization-corrected metallicity using cloudy photoionization models. The H i column density ranges from ∼1013 to ∼1020 cm−2 and decreases with impact parameter for r ≳ R e . Galaxies with higher stellar mass have weaker H i absorption. Comparing absorption velocities with MaNGA radial velocity maps of ionized gas line emissions in galactic disks, we find that the neutral gas seen in absorption corotates with the disk out to ∼10 R e . Sight lines with lower elevation angles show lower metallicities, consistent with the metallicity gradient in the disk derived from MaNGA maps. Higher-elevation angle sight lines show higher ionization, lower H i column density, supersolar metallicity, and velocities consistent with the direction of galactic outflow. Our data offer the first detailed comparisons of circumgalactic medium (CGM) properties (kinematics and metallicity) with extrapolations of detailed galaxy maps from integral field spectroscopy; similar studies for larger samples are needed to more fully understand how galaxies interact with their CGM.

Improving the wet mapping function by numerical weather models

In space geodetic techniques, the mapping functions (MFs) provide the relationship between zenith and slant tropospheric delays. The MFs are determined under the assumption of spherically layered atmosphere. However, the atmosphere is not spherically layered, and the asymmetry should be considered. Therefore, tropospheric gradients are taken into account. Nevertheless, tropospheric gradients alone can not fully represent the deviation from a spherically layered atmosphere, and hence cm level errors arise especially for low elevation angles. In this study, we present new approaches to modify the wet MF to reduce mismodelling of tropospheric delays. The delays in the study were calculated using ray-tracing algorithm based on ECMWF’s ERA5 dataset. We first analyzed the performances of the new approaches. Then, two Precise Point Positioning (PPP) simulation studies and a real case study were carried out for two different regions namely Germany and Türkiye. According to the results, the proposed approaches reduce the modelling errors up to by a factor 6 for both regions. Besides, simulation studies show that the approaches improve the accuracies of the ZTDs and heights. In the practical application however, we could not find a clear improvement in the PPP analyze and this might be related to the ERA5 which can not be regarded error-free.

Ground-to-Air Tropospheric Mapping Function for Very Low Elevation Angles

This paper proposes a real-time capable tropospheric delay model for terrestrial radio navigation systems used for aviation. Its functional scope ranges from elevation angles below the local horizon to zenith. Flight experiments were carried out to quantify the improvement in service coverage achieved for measurements close to and below the local horizon, with aircraft distances in the order of 250 km. Mismodeling tropospheric delays at these elevation angles and aircraft distances can result in slant-range error several order of magnitude greater than the accuracy of terrestrial nav-aids, and adequately accounting them translates into improved accuracy and tighter integrity bounds. The proposed method uses a polynomial representation of the atmospheric refractivity instead of the traditional exponential distribution used in GNSS. The resulting method provides tropospheric corrections accurate to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 0.5 cm for elevation angles above 5 degrees, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula> 15 cm at an elevation of 0.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> . In addition, the proposed model offers a reduction in the horizontal position error in terms of an order of magnitude from 14 meters (for uncompensated tropospheric delay) to below 1.6 cm for all flight segments, that will enable terrestrial systems to support increasingly demanding performance based navigation systems.

Development of a Cadaveric Shoulder Motion Simulator with Open-Loop Iterative Learning for Dynamic, Multiplanar Motion: A Preliminary Study.

Ex vivo shoulder motion simulators are commonly used to study shoulder biomechanics but are often limited to performing simple planar motions at quasi-static speeds using control architectures that do not allow muscles to be deactivated. The purpose of this study was to develop an open-loop tendon excursion controller with iterative learning and independent muscle control to simulate complex multiplanar motion at functional speeds and allow for muscle deactivation. The simulator performed abduction/adduction, faceted circumduction, and abduction/adduction (subscapularis deactivation) using a cadaveric shoulder with an implanted reverse total shoulder prosthesis. Kinematic tracking accuracy and repeatability were assessed using maximum absolute error (MAE), root mean square error (RMSE), and average standard deviation (ASD). During abduction/adduction and faceted circumduction, the RMSE did not exceed 0.3, 0.7, and 0.8 degrees for elevation, plane of elevation, and axial rotation, respectively. During abduction/adduction, the ASD did not exceed 0.2 degrees. Abduction/adduction (subscapularis deactivation) resulted in a loss of internal rotation, which could not be restored at low elevation angles. This study presents a novel control architecture, which can accurately simulate complex glenohumeral motion. This simulator will be used as a testing platform to examine the effect of shoulder pathology, treatment, and rehabilitation on joint biomechanics during functional shoulder movements.

Insights on Polar Day Antarctica Radio Propagation Using Amateur Radio Beacons on Circumnavigating Balloons

We deployed six pico balloons with 20 m transmitters (14.09 MHz) from Neumayer Station III in the 2022 Antarctic summer. Our objective was to evaluate ionospheric propagation in lower latitudes. Leveraging the Weak Signal Propagation Reporter (WSPR) protocol, we transmitted and received telemetry data on a global scale. Each balloon remained airborne for over a month, with one completing eight circumnavigations of the southern hemisphere, transmitting WSPR beacon data for 98 days. Our analysis focused on signal propagation characteristics in the polar ionosphere and surrounding regions, considering factors such as location relative to the WSPR network and solar elevation angles. Alignment between solar elevation angles at transmitting and receiving stations indicated a relationship with signal reception; lower solar elevation angles proved crucial for long-range propagation. We discovered that, beyond a solar angle of 60 degrees above the horizon, no decodes were recorded beyond 7500 km. Most signal spots were observed within a 1000–5000 km range and solar elevation angles ranging from 1 to 80 degrees. Over Antarctica, spot occurrences peaked around 4 UTC, particularly during the early hours of the day. Our findings demonstrate the usefulness of pico balloons for propagation studies, providing insights into the WSPR network’s coverage over Antarctica and surrounding lower latitudes.

Evaluation of L-band GPS signal attenuation to multiple vegetations using ground-based measurements

ABSTRACT Global Navigation Satellite System Reflectometry (GNSS-R) is a remote sensing technique that can be regarded as a bistatic radar system. GNSS-R uses GNSS signals as signal sources and obtains the Earth’s surface environmental parameters, such as soil moisture (SM), by receiving the L-band microwave signal reflected from the Earth’s surface. However, surface vegetation could be one of the main factors influencing the accuracy of GNSS-R land applications since plants, including branches and leaves, attenuate GNSS signals. Additionally, the evaluation of signal attenuation caused by the plant canopy is quite difficult. In this paper, we study the attenuations of received L1- and L2-band GPS signals to the vegetation leaf area index (LAI) for different types of plants. The relationship between the attenuation of the GPS signal-to-noise ratio (SNR) (both above and below the canopy) and the LAI is established through field experiments. The results show that the mean SNR received in the L2 band is lower than that in the L1 band for each satellite but with a larger standard deviation (SD). The sensitivities of L1- and L2-band signals to the LAI are revealed, revealing greater sensitivity and a relatively good Pearson correlation coefficient (R) for lower elevation angles and vegetation biomass. In addition, the sensitivity and R of L2-band signals to the LAI are lower than those of L1-band signals. This study is significantly valuable for improving the quantitative representation of error estimates for GNSS-R SM retrieval. The established model can be employed in GNSS land applications and aid in solving signal surface-scattering problems in which accurate signal estimates are important.

Reducing Ground Reflection Multipath Errors for Bluetooth Angle-of-Arrival Estimation by Combining Independent Antenna Arrays

For outdoor navigation using Bluetooth direction finding, elevation angle estimate errors due to ground reflection multipath interference is a significant challenge at low elevation angles. One of the ways to reduce this issue is to increase the vertical dimension of the array. We consider the synchronization of measurements from two independent arrays stacked vertically to achieve the same effect without needing to construct a larger array, allowing hardware modularity using low-cost equipment. The measurement synchronization is itself affected by the multipath, and a method to handle this effect is proposed. Using measurements from a 15 cm x 15 cm array in field experiments, we demonstrate a reduction in elevation error of up to 10° at elevation angles in the 7° to 15° range, where the error was largest when using a single array.

Detection of dawn sea fog/low stratus using geostationary satellite imagery

Traditional satellite-based detection of dawn sea fog/low stratus (SFLS) is difficult because of the weak reflectivity in the visible at low solar elevation angles and the contamination of the reflected sunlight in the mid-infrared. Here, based on single geostationary satellite measurements acquired by China's Fengyun 4A (FY-4A), we propose a dawn SFLS detection algorithm using the joint Fully Convolutional Network and Conditional Random Field (FCN-CRF), which are well known for image semantic segmentation under low contrast conditions. We train the FCN-CRF detection algorithm using FY-4A measurements over the Yellow Sea, where some dawn SFLS events are long-lived, providing relatively time-invariant dawn SFLS samples for training. We design a SFLS labelling technique using the satellite observations before and after dawn to train the FCN-CRF detection for dawn SFLS. A test against buoy visibility observations shows that the FCN-CRF detection is able to detect dawn SFLS with satisfactory accuracy, with a probability of detection (POD) of 84.9%, a false alarm ratio (FAR) of 8.7%, a critical success index (CSI) of 78.5% and a hit rate score (HR) of 87.4%.

Improved estimation of hourly direct normal solar irradiation (DNI) using geostationary satellite visible channel images over moderate albedo areas

An accurate knowledge of the direct solar irradiance at normal incidence (DNI) is required to size solar energy systems, specially those using solar concentration technologies. In the absence of measurements, DNI can be estimated over an arbitrary site with a dedicated satellite model or by using satellite-derived global horizontal irradiance (GHI) and a phenomenological diffuse-direct separation model. This second procedure is error-prone, specially under partial cloudiness conditions and low solar elevation angles. A novel and simple semi-empirical satellite-based model to estimate DNI in moderate albedo regions using a physical clear sky model and a cloudiness index obtained from visible satellite imagery is proposed and assessed. An ergodic assumption in which the images are spatially averaged to better represent the hourly time basis is used. Over the target region (Southeastern South America, SESA), the new DNI satellite model outperforms the alternative strategy at the hourly level, with an average uncertainty of 20% (versus 25%) when compared with three measurement station’s data sets located in center Argentina, southern Brazil and Uruguay.

Incipient anomalous ionospheric divergence fast detection for coastal differential Global Navigation Satellite System

Differential Global Navigation Satellite System (DGNSS) plays an increasingly important role in the maritime field. Irregular ionospheric divergences may result in DGNSS performance degradation and increase risk in terms of positioning accuracy and navigation integrity. To speed up incipient ionospheric anomaly detection, this paper proposes a novel method for the DGNSS stations which employs (1) the Wasserstein distance (WD) to identify dissimilarity between GNSS pseudorange and carrier-phase measurements and (2) the least-mean-square (LMS) filter to smooth the calculated metrics. The combined WD-LMS is proposed to ensure the rapid identification of abnormal ionospheric divergences. Taking the multipath into account, which is especially severe in the low elevation angle case, elevation-angle related strategies are developed. Both semi-simulated and real experiments are conducted. For the high-elevation angle case, the WD-LMS is even potential to detect large ionospheric divergences within ten epochs. Therefore, the WD-LMS has encouraging potential to enhance maritime DGNSS navigation performance.

Characterization of prosthetic knees through a low-dimensional description of gait kinematics

The characterization of both limbs’ behaviour in prosthetic gait is of key importance for improving the prosthetic components and increasing the biomechanical capability of trans-femoral amputees. When characterizing human gait, modular motor control theories have been proven to be powerful in providing a compact description of the gait patterns. In this paper, the planar covariation law of lower limb elevation angles is proposed as a compact, modular description of prosthetic gait; this model is exploited for a comparison between trans-femoral amputees walking with different prosthetic knees and control subjects walking at different speeds. Results show how the planar covariation law is maintained in prostheses users, with a similar spatial organization and few temporal differences. Most of the differences among the different prosthetic knees are found in the kinematic coordination patterns of the sound side. Moreover, different geometrical parameters have been calculated over the common projected plane, and their correlation with classical gait spatiotemporal and stability parameters has been investigated. The results from this latter analysis have highlighted a correlation with several parameters of gait, suggesting that this compact description of kinematics unravels a significant biomechanical meaning. These results can be exploited to guide the control mechanisms of prosthetic devices based purely on the measurement of relevant kinematic quantities.

Retrievals of precipitable water vapor and aerosol optical depth from direct sun measurements with EKO MS711 and MS712 spectroradiometers

Abstract. Based on the strict radiative transfer algorithm, a new method is developed to derive the precipitable water vapor (PWV) and aerosol optical depth (AOD) from the ground-based direct sun irradiance measurements. The attenuated direct irradiance from 300 to 1700 nm was measured by a pair of grating spectroradiometers, MS711 and MS712 produced by EKO Instruments, located at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing (39.98∘ N, 116.38∘ E), from June 2020 to March 2021. Compared with regular sun photometers such as CE-318 and POM, EKO instruments can measure a wider range of continuous spectra, but their field of view (FOV) is also relatively large. In the PWV inversion of this work, a strong water vapor absorption band around 1370 nm is introduced to retrieve PWV in a relatively dry atmosphere. The circumsolar radiation (CSR) of the EKO instruments is corrected to reduce the influence of scattering from a relatively larger FOV on the AOD inversion. The PWV and AOD inversion results obtained by MS711 and MS712 are compared with the synchronous data of the CE-318 sun photometer. The two retrieval results are highly consistent. The correlation coefficient, mean bias, and standard deviation of PWVEKO and PWVCIMEL are 0.999, −0.027 cm (−2.42 %), and 0.054 cm (3.93 %), respectively, and the relative deviations of the differences between the two are slightly larger for drier air (PWV &lt; 0.5 cm) and lower solar elevation angle. The correlation coefficients of AODEKO and AODCIMEL at 380, 440, 500, 675, 870, and 1020 nm are greater than 0.99, and the relative deviations vary between −6.59 % and 4.27 %.

Analysis of a Low-Earth Orbit Satellite Downlink Considering Antenna Radiation Patterns and Space Environment in Interference Situations

This paper investigates a low-Earth orbit (LEO) satellite downlink for high-speed data communication in interference situations. A choke ring horn type antenna is used as the data transmitting antenna with an isoflux pattern in the LEO satellite, which has a beam coverage of ±51.6° and a bore-sight gain of 4.4 dBi at 8 GHz. The receiving antenna on the ground station is a parabolic type antenna with a diameter of 11.3 m, and it has a half-power beam width (HPBW) of 0.2° with a maximum gain of 59 dBi at 8 GHz. The jamming-to-signal ratio (J/S) is calculated assuming that the LEO satellite transmits signals to the ground station, and an elevation angle of the interference source varies from 0° to 90° at an altitude of 10 km. Applying antenna characteristics, such as HPBWs and side lobes, to the calculated space wave path loss makes it possible to predict the J/S results according to the location of the interference source and the satellite. The results show that it is necessary to consider the space environment to accurately analyze the LEO satellite downlink, especially at the low elevation angle of the satellite.