Satellite Bands Research Articles

Estimation of global and diffuse horizontal irradiance by machine learning techniques based on variables from the Heliosat model

The increased interest in the sources of renewable electricity has drawn attention to the rapidly developing solar energy sector owing to its high cost-benefit ratio. To accurately calculate the potential electricity output of photovoltaic (PV) panels, the global horizontal irradiance (GHI) and diffuse horizontal irradiance (DHI) must be known. The worldwide presence of satellite imagery provides an efficient way to estimate current and historical GHI instead of using the high time- and cost-consuming in-situ measurement. The most of past studies utilized more satellite bands as the inputs for machine learning algorithms to estimate GHI. The further estimation of DHI was usually based on weather-related parameters. Thus, there is a research gap in using only one satellite band for both GHI and DHI estimations. Therefore, this study used machine learning algorithms to estimate GHI and DHI, with inputs delivered from the Heliosat model based on band 3 of Himawari-8 satellite imageries. The results were compared with the original and site-adapted Heliosat models and seven DHI separation models. The results indicated that the machine learning models were capable of performing with the same accuracy as the Heliosat models. However, their performance was better while estimating DHI, in which case they outperformed even the best separation model. Higher accuracy and precision were observed in those models where the additional solar zenith at time t+1h was used together with other input features. This highlighted the possibility of using only one satellite band together with the calculated solar position variables as the input. Overall, this research has established a new method for estimating GHI and DHI with high confidence based on satellite imageries and the Heliosat model through the application of machine learning techniques.

Remote sensing to detect harmful algal blooms in inland waterbodies

Harmful algal blooms (HABs) are an issue of concern for water management worldwide. As such, effective monitoring strategies of HAB spatio-temporal variability in waterbodies are needed. Remote sensing has become an increasingly important tool for HAB detection and monitoring in large lakes. However, accurate HAB detection in small-medium waterbodies via satellite data remains a challenge. Current barriers include the waterbody size, the limited freely available high resolution satellite data, and the lack of field calibration data. To test the applicability of remote sensing for detecting HABs in small-medium waterbodies, three satellites (Planetscope, Sentinel-2 and Landsat-8) were used to understand how spatial resolution, the availability of spectral bands, and the waterbody size itself effect HAB detection skill. Different algorithms and a non-parametric method, Self-Organizing Map (SOM), were tested. Curvature Around Red and NIR minus Red had the best HAB detection skill of the 20 existing algorithms that were tested. Landsat 8 and Sentinel 2 were the best satellites for HAB detection in small to medium waterbodies. The most critical attribute for detecting HABs were the available satellite bands, which determine the detection algorithms that can be used. Importantly, algorithm performance was mostly unrelated to waterbody size. However, there remain some barriers in utilizing satellite data for HAB detection, including algae dynamics, macrophyte cover within the waterbody, weather effects, and the correction models for satellite data. Moreover, it is important to consider the match time between satellite overpass and sampling activities for calibration. Given these challenges, integrating regular sampling activities and remote sensing is recommended for monitoring and managing small-medium waterbodies.

A 5-W GaN Doherty Amplifier for Ka-Band Satellite Downlink With 4-GHz Bandwidth and 17-dB NPR

This letter presents the design and experimental characterization of a GaN–Si monolithic Doherty power amplifier (PA) for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Ka$ </tex-math></inline-formula> -band satellite downlink. The fabricated amplifier favorably compares with the current state of the art, achieving from 16.3 to 20.3 GHz (4 GHz, 22% relative bandwidth), a record band to date, 36.6–37.7-dBm output power, 23%–31% power-added efficiency, 18–22-dB gain at saturation, and around 20% power-added efficiency at 6-dB output back-off. At 18.8 GHz, the amplifier shows a noise-to-power ratio higher than 17 dB at all power levels, making it suitable for satellite applications where additional linearization is usually unfeasible.

Land Surface Temperature Regulation Ecosystem Service: A Case Study of Jaipur, India, and the Urban Island of Jhalana Reserve Forest

Although Land Surface Temperatures (LSTs) are on the rise globally, the distribution of LSTs varies depending on the land cover type. Urban Heat Island and Urban Cool Island effects act differently, especially in semi-arid regions. Therefore, we identify demi-decadal, seasonal, and zonal differences in LSTs in a semi-arid region in the city of Jaipur, where zones include rural and urban areas that encircle the Jhalana Reserve Forest (JRF). After deriving LSTs from remotely sensed thermal bands of Landsat satellites’ Multi-spectral datasets, we found that there is a significant difference in LST (p &lt; 0.01) among the zones. In addition, LSTs were found to be significantly lower in JRF compared to Urban and Rural areas in all seasons and all study years, which indicates the urban cooling effect due to the presence of the forest. Nevertheless, summer LSTs have warmed with a mean difference of 4.8 °C between 2000 and 2020. Therefore, our study supports the promotion of Urban Forests, especially in semi-arid zones, for inculcating LST regulation ecosystem services to enrich and enhance the standard of living of the human population.

Multi-sensor and multi-platform consistency and interoperability between UAV, Planet CubeSat, Sentinel-2, and Landsat reflectance data

ABSTRACT Unmanned aerial vehicle (UAV) and satellite data have considerable complementarity for platform inter-operability, data fusion studies, calibration and validation efforts, and various multiscale analyses. To optimize cross-platform synergies between field-deployable UAV and space-based satellite systems, an understanding of spectral characteristics and compatibility is required. Here, we present the assessment of spectral consistency, undertaking a pixel-to-pixel similarity assessment of co-registered reflectance maps using corresponding spectral bands from UAV and satellite multispectral imagery. A high-resolution centimeter-scale UAV-mounted MicaSense RedEdge-MX sensor is intercompared against variable-resolution multi-spectral sensors on-board PlanetScope, Sentinel-2 and Landsat 8 platforms. Sampling from within an urban environment that covers a range of both natural and man-made surfaces, we employ ground-based spectroradiometer data to evaluate pixel-level responses, using regression analysis and measurements of relative root mean square error (rRMSE) to assess for factors such as spatial and spectral misalignment. Using two radiometric correction approaches for the UAV data, we found that a vicarious radiometric correction was more accurate than a linear empirical line method, with the former improving rRMSE by between 1.6% and 20.11% when assessed against spectroradiometer measurements. Spectral band misalignment between the UAV and satellite sensors affected their spectral consistency, causing different reflectance values for the same object in the corresponding UAV and satellite bands, with the issue amplified over specific land-cover classes (e.g. grass in the red edge part of the spectrum). Using the standard deviation of a UAV-derived normalized difference vegetation index (NDVI) as a metric of spatial heterogeneity, larger differences between the UAV and satellite-based NDVI were observed for different ground features in response to both land-cover boundary and shadow effects. Interestingly, higher spatial heterogeneity did not necessarily lead to higher spectral inconsistencies. It was also determined that as spatial scale differences between the UAV and satellite platforms increased, the lower was the impact of geometric misregistration on their consistency. Indeed, the rRMSE between the reflectance values of the UAV-based spectral bands and the corresponding satellite imagery was smaller at lower resolution (e.g. Landsat 8) than higher resolution (e.g. PlanetScope). Overall, the study provides insight into the collective effect of spectral and spatial misalignments on the degree of spectral consistency that can be expected between UAV and satellite data, guiding robust radiometric intercalibration efforts and the potential for improved synergy and interoperability between UAV and satellite data.

Polarization insensitive split square ring resonator based epsilon-negative and near zero refractive index metamaterial for S, C, and X frequency bands satellite and radar communications

This study has investigated the impact of inverse G-like shape resonators that exhibited epsilon negative (ENG) and near-zero refractive index (NZI) properties for multi-band wireless communications applications. The electrical measurement of structure is 0.118λ × 0.118λ × 0.021 λ, which is calculated at 3.94 GHz. FR-4 is used as a substrate layer, and the resonator is designed on it. This structure is manifested in the ENG and NZI characteristics within the frequency range of 3.8–4.17, 7.68–8.54, 10.67–11.36 GHz, and 4.07–4.15 and 8.29–8.37 GHz, respectively. This study also manifests the polarization insensitivity nature of 0°–90°, and the incident angle is investigated up to 60° for both TE and TM modes. The proposed structure achieves triple resonance at 3.94 GHz, 8.08 GHz, and 11.17 GHz, respectively, included in the S, C, and X frequency bands. The CST Microwave Studio 2019 software is conducted to design, develop, perform analysis, investigate electromagnetic properties, and extract effective medium parameters. The Advanced Design Software (ADS) is used to model the equivalent circuit of the unit cell. The simulated, measured, and ADS results verified the scattering parameter performance. The EMR value of the structure is 8.47, indicating the structure's compactness. The compact design with simplicity, ENG, and NZI properties make the proposed structure significant for microwave application, mainly to enhance the antenna bandwidth and gain filter design. ENG and NZI properties the operation frequency stability and efficiency for low earth orbit nanosatellite communications.

Efficient Uplink Transmission in Ultra-Dense LEO Satellite Networks With Multiband Antennas

In this letter, we propose an efficient uplink transmission scheme over ultra-dense low earth orbit (LEO) satellite networks with multiband antennas. A two-timescale transmission resource allocation and frequency band switching optimization framework is established with the objective of maximizing the overall data rate while reducing the band switching cost. The small-timescale transmission resource allocation problem is described as a Markov decision process (MDP) considering continuous LEO satellite movements and Markovian rainfall changes, while the large-timescale satellite band switching is formulated as an integer programming problem. A hierarchical algorithm based on the deep reinforcement learning (DRL) approach and the greedy method is proposed to make efficient decisions. Extensive simulations are conducted to validate the effectiveness and advantages of our proposed scheme.

Estimation of Soil Texture and Amount of Free Iron Oxides Using Landsat 8 Satellite Bands and Regression Analysis

این پژوهش با هدف برآورد ویژگی‌های خاک، با استفاده از باندهای ماهوارة لندست 8، در بخشی از زمین‌های زراعی دشت قروه‌ـ دهگلان در غرب ایران انجام شد. در مجموع، از 107 نقطة محدودة مطالعاتی، از عمق 15-0 سانتی‌متری نمونة خاک تهیه و ویژگی‌های فیزیکوشیمیایی این نمونه‌ها در آزمایشگاه اندازه‌گیری شد. برای استخراج اطلاعات از تصویر ماهوارة لندست 8 و پس از اعمال ماسک پوشش گیاهی، مقادیر DOS باندهای 7-1 برای نقاط نمونه‌برداری استخراج شد. به‌منظور تعیین رابطة بین ویژگی‌های خاک و ارزش رقومی باندهای لندست 8، تحلیل همبستگی، رگرسیون خطی گام‌به‌گام و رگرسیون مؤلفة اصلی به‌کار رفت. اعتبارسنجی تحلیل رگرسیون‌ها با استفاده از دو پارامتر ضریب تعیین و ریشة میانگین مربعات خطا ارزیابی شد. نتایج نشان داد که همبستگی مثبت و معنی‌داری بین مقادیر شن و اکسیدهای آزاد آهن خاک و همبستگی منفی و معنی‌داری بین رس و سیلت خاک، با ارزش رقومی بیشتر باندهای لندست 8، وجود دارد. بین غلظت فلزات سنگین و ارزش رقومی در باندهای مرئی و مادون قرمز نزدیک، همبستگی معنی‌داری مشاهده نشد و تحلیل‌های رگرسیون نیز، در برآورد ویژگی‌های خاک محدودة مطالعاتی، کارآیی مورد قبولی نداشت. با توجه به نتایج، به‌نظر می‌رسد که می‌توان از تصاویر ماهوارة لندست 8 به‌منظور برآورد بافت خاک و مقادیر اکسیدهای آزاد آهن خاک، در محدودة مورد مطالعه، استفاده کرد.

EFFECTS OF GF-6 SATELLITE RED-EDGE BANDS ON PEANUT DROUGHT MONITORING

Abstract. Red-edge band is an indicator band to describe the health status of crops. In order to explore the impact of the red-edge bands on the accuracy of agricultural drought monitoring, this study used GF-6 WFV and Landsat8 to calculate the Red-edge Normalized Difference Vegetation Index (NDVI705), Vogelmann red-edge index 1 (VOG1), Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST) to construct temperature vegetation drought index (TVDI), this index integrated vegetation index and land surface temperature information, the soil relative humidity data and the measured drought grade data were respectively used for correlation analysis and classification accuracy verification of the TVDI results. The results showed that dry edge equation fit with red edge bands were higher than that of non-red edge bands. The dry edge equation based on VOG1 index has the highest fit, with a maximum coefficient determination of 0.92; TVDI constructed by the above vegetation index have significant negative correlation with soil relative humidity. The TVDI based on the VOG1 index has a better correlation with the relative soil humidity, with a maximum correlation coefficient of 0.85; and realized the dynamic monitoring of peanut drought grade, the overall accuracy rate of peanut drought grade monitoring reached 92.59%, and the result of TVDI classification was in good agreement with the actual drought grade measurement result. The red edge bands of GF-6 satellite can effectively improve the accuracy of peanut drought monitoring and better characterize peanut drought information. This research provides a data reference for the application of GF-6 WFV data in agricultural drought monitoring.

The circularly bent split ring resonator with a high effective medium ratio for multi frequency satellite band applications

The scattering parameter for the interaction with the electromagnetic wave is introduced the interesting properties of the effective parameter. The compactness of the subwavelength based metal-dielectric based resonator is related to the tailored metallic design. In this research work, two circular bent split ring resonator is represented with four resonant frequencies for S, C band applications. This subwavelength based metamaterial resonator exhibit the bandwidth from 1.97 to 2.11, 3.43–3.63, 5.31–5.46, 8.3–8.6 GHz at 2.03, 3.57, 5.37, 8.47 GHz, respectively. The geometric specification, equivalent circuit model, design selection process are included to observe the electromagnetic characteristics, and the electric field, magnetic field and surface current distribution are used to analyse the state of polarisation at different resonant frequencies for the applied transverse electromagnetic wave. In parametric analysis, the relative angular rotation of two bent circular split resonators expresses the effect of the metallic layer with the rearrangement of the gap between the conducting layers. Moreover, different substrate materials with a change in thickness are analysed to characterize the scattering properties for different dielectric constants.

A circularly polarized folded reflectarray antenna for Ka‐band satellite communications uplinks

AbstractA low‐profile circularly polarized folded reflectarray antenna (CPFRA) with linearly polarized (LP) feed antenna is presented in this article. Polarizing grid usually used as the subreflector of traditional FRA is replaced by a polarization‐sensitive frequency selective surface (FSS) in the CPFRA design. The polarization‐sensitive FSS is designed to convert the LP incidence into the CP wave within its passband while reflecting the orthogonal LP incident wave over its operating frequency band. A CPFRA prototype has been proposed and validated for Ka band satellite communications uplinks in this article. The maximum measured antenna gain of 26.0 dBic is achieved at 29.75 GHz with the corresponding antenna aperture efficiency of 40%. Beam scanning property has been achieved by the CPFRA with the mechanical movement of feed horn antenna. All the measured axial ratios (ARs) of the CPFRA are lower than 3 dB in the frequency range from 29 to 30.25 GHz. Meanwhile, the measured antenna gain variation with different beam scanning angles is less than 1 dB from 29.25 to 31 GHz.

Increase of Radiative Forcing through Midinfrared Absorption by Stable CO2 Dimers?

We performed matrix-isolation infrared (MI-IR) spectroscopy of carbon dioxide monomers, CO2, and dimers, (CO2)2, trapped in neon and in air. On the basis of vibration configuration interaction (VCI) calculations accounting for mode coupling and anharmonicity, we identify additional infrared-active bands in the MI-IR spectra due to the (CO2)2 dimer. These bands are satellite bands next to the established CO2 monomer bands, which appear in the infrared window of Earth’s atmosphere at around 4 and 15 μm. In a systematic carbon dioxide mixing ratio study using neon matrixes, we observe a significant fraction of the dimer at mixing ratios above 300 ppm, with a steep increase up to 1000 ppm. In neon matrix, the dimer increases the IR absorbance by about 15% at 400 ppm compared to the monomer absorbance alone. This suggests a high fraction of the (CO2)2 dimer in our matrix experiments. In atmospheric conditions, such increased absorbance would significantly amplify radiative forcings and, thus, the greenhouse warming. To enable a comparison of our laboratory experiment with various atmospheric conditions (Earth, Mars, Venus), we compute the thermodynamics of the dimerization accordingly. The dimerization is favored at low temperatures and/or high carbon dioxide partial pressures. Thus, we argue that matrix isolation does not trap the gas composition “as is”. Instead, the gas is precooled to 40 K, where CO2 dimerizes before being trapped in the matrix, already at very low carbon dioxide partial pressures. In the context of planetary atmospheres, our results improve understanding of the greenhouse effect for planets of rather thick CO2 atmospheres such as Venus, where a significant fraction of the (CO2)2 dimer can be expected. There, the necessity of including the mid-IR absorption by stable (CO2)2 dimers in databases used for modeling radiative forcing, such as HITRAN, arises.

Modified Coptic Cross Shaped Split-Ring Resonator Based Negative Permittivity Metamaterial for Quad Band Satellite Applications with High Effective Medium Ratio.

This research article describes a modified Coptic cross shaped split ring resonator (SRR) based metamaterial that exhibits a negative permittivity and refractive index with a permeability of nearly zero. The metamaterial unit cell consists of an SRR and modified Coptic cross shaped resonator providing quadruple resonance frequency at 2.02, 6.985, 9.985 and 14.425 GHz with the magnitude of −29.45, −25.44, −19.05, and −24.45 dB, respectively. The unit cell that was fabricated on a FR-4 substrate with a thickness of 1.6 mm has an electrical dimension of 0.074λ × 0.074λ; the wavelength (λ) is computed at the frequency of 2.02 GHz. The computer simulation technology (CST) microwave studio was employed to determine the scattering parameters and their effective medium properties, i.e., permittivity, permeability and refractive index, also calculated based on NRW (Nicolson–Ross–Weir) method through the implementation of MATLAB code. The frequency range of 2.02–2.995 GHz, 6.985–7.945 GHz, 9.985–10.6 GHz, and 14.425–15.445 GHz has been found for negative permittivity. An effective medium ratio (EMR) of 13.50 at 2.02 GHz shows that the proposed unit cell is compact and effective. The lumped component based equivalent circuit model is used to validate with simulation results. The proposed unit cell and its array were fabricated for experimental verification. The results show that the simulation result using CST and high-frequency structure simulator (HFSS) simulator, equivalent circuit model result using advanced design system (ADS) simulator and measurement results match each other better. Its near zero permeability, negative permittivity, negative refractive index, high EMR and simple unit cell design allow the proposed metamaterial to be used for S-, C-, X- and Ku-band satellite applications.

Optimization of Parallel Coupled Filter Using Genetic Algorithm for C Band Applications

PCML filter with five coupled lines is designed using mathematical calculations then the same PCML filter is optimized using GA for reduction in size and bandwidth enhancement. Optimized filter is compact and total size reduction is 37.66% after optimization and bandwidth enhancement after optimization is 84.3%. Both filters are useful for C band applications, wireless communication, satellite communication, cordless phones, surveillance, and weather monitoring using weather radar. The substrate used is FR4 epoxy with a dielectric constant 4.4 and thickness 1.6 mm.

The Application of Satellite Image Analysis in Oil Spill Detection

In recent years, there has been an increasing use of satellite sensors to detect and track oil spills. The satellite bands, namely visible, short, medium infrared, and microwave radar bands, are used for this purpose. The use of satellite images is extremely valuable for oil spill analysis. With satellite images, we can identify the source of leakage and assess the extent of potential damage. However, it is not yet clear how to approach a specific leakage case methodologically. The aim of this study is the remote sensing analysis of environmental changes with the development of oil spill detection processing methods. Innovative elements of the work, in addition to methodological proposals, include the long-term analysis of surface water changes. This is very important because oil is very likely to enter the soil when water levels change. The classification result was satisfactory and accurate by 85%. The study was carried out using images from Landsat 5, Landsat 7, Landsat 8, Sentinel-1, and Sentinel-2 satellites. The results of the classification of the oil stains in active and passive technologies differ. This difference affects the methodology for selecting processing methods in similar fields. In the case of this article, the oil spill that occurred on 29 May 2020 in Norilsk was investigated and compared with data from other years to determine the extent of biodegradation. Due to the tank failure that occurred at the Nornickel power plant on that day, a large amount of crude oil leaked into the environment, contaminating the waters and soil of local areas. Research shows that oil spills may be caused by human error or may be the effect of climate change, particularly global warming.

Wide bandwidth enriched symmetric hexagonal split ring resonator based triple band negative permittivity metamaterial for satellite and Wi-Fi applications

Bandwidth is a vital factor for the transmission phase of satellite data that plays an important role in satellite performance. This paper presents a wide bandwidth enriched metamaterial consisting of symmetric hexagonal split ring resonator (SRR) with triple band negative permittivity and refractive index and near zero permeability for satellite and Wi-Fi applications. The electrical dimension of the designed metamaterial unit cell is 0.17λ × 0.17λ where wavelength (λ) is computed at a first resonance frequency and developed on a cheap dielectric material FR-4 (lossy) with a thickness of 1.6 mm. The proposed metamaterial contributes triple resonances for the transmission coefficient (S21) at the frequencies of 5 GHz, 6.88 GHz and 8.429 GHz with the magnitude of −33.79, −21.7 and −25.18 dB, respectively covering C and X bands through the numerical execution of CST microwave studio 2019. The effective bandwidth of the unit cell are 1.67 GHz (3.89 to 5.56 GHz), 0.52 GHz (6.59 to 7.11 GHz) and 0.98 GHz (7.98 to 8.96 GHz) where the value of S21 less than −10 dB. The first resonance frequency is used to high speed-bandwidth enriched Wi-Fi and satellite band. Wi-Fi is usually faster using 5 GHz frequency band. The rest of the resonance frequency can be used in satellite applications. A negative permittivity has been perceived at frequencies of 5 – 6.066 GHz, 6.88 – 7.409 GHz, 8.429 – 10.061 GHz using Nicolson-Ross-Weir (NRW) methods with MATLAB code. The dependence of the resonance frequencies on the design parameters, substrate thickness, dielectric materials, the influence of the different structure of unit cell has also been examined. The designed unit cell structure with equivalent circuit diagram are analyzed and validated using Advanced Design System (ADS) simulator that exhibits similar to the S21 of the proposed structure. Furthermore, measurement results and Ansys high-frequency structure simulator (HFSS) simulator results are also employed to verify the outcome. Due to the overall performance, such as wide bandwidth, excellent effective parameters of the designed structure, the proposed research can be very suitable for satellite and Wi-Fi applications.

A New Compact Split Ring Resonator Based Double Inverse Epsilon Shaped Metamaterial for Triple Band Satellite and Radar Communication

This study presents a double-inverse-epsilon-shaped, triple-band epsilon-negative (ENG) metamaterial with two split ring resonators (SRRs). The proposed unit cell comprises a single slit two SRRs with two inverse-epsilon-shaped metal bits. Rogers RT6002, of dimension 10 × 10 × 1.524 mm3, is used as a substrate. An electromagnetic simulator CST microwave studio is used to investigate the effective medium parameters of the material. The proposed metamaterial shows three resonance peaks that are demarcated at the frequencies 2.38 GHz, 4.55 GHz and 9.42 GHz consecutively. The negative permittivity of the metamaterial is observed at the frequency ranges of 2.39–2.62 GHz, 4.55–4.80 GHz and 9.42–10.25 GHz. The goodness of the material was presented by the effective medium ratio (EMR) of the unit cell at 12.61. In addition, the simulated results are authenticated by using different electromagnetic simulators such as HFSS and ADS for the equivalent circuit model, which exhibits insignificant disparity. The anticipated scheme was finalised through some parametric analyses, together with configuration optimisation, different unit cell dimensions, several substrate materials, and altered electromagnetic (EM) field transmissions. The proposed triple band (S-, C- and X-bands) with negative permittivity (ε) metamaterial is practically used for numerous wireless uses, for instance, far distance radar communication, satellite communication bands and microwave communication.

Impact of Land-use Change on Agricultural Production &amp; Accuracy Assessment through Confusion Matrix

Land modification and its allied resources have progressively become a severe problem presently pulling the worldwide attention and now it rests at the central point of the conservation of the environment and sustainability. The present research aimed to examine the land-use changes and their impact on agricultural production using remote sensing and GIS techniques over the study area that comprised of Tehsil Shorkot, District Jhang, Punjab, Pakistan. Images were pre-processed by using the Arc GIS and ERDAS Imagine 15 software for stacking of the layers, sub-setting, and mosaicking of the satellite bands. After the pre-processing of the images, supervised image classification scheme was applied by employing a maximum likelihood algorithm to recognize the land-use changes which have been observed in the area under study. The area under water was occupied 9.6 km2 in 2010 that increased to 21.04 km2 in 2015 and decreased to 19.4 km2in 2020. Built-up land was 16.6 km2 in 2010 that increased to 19.4 km2 in 2015 and 26.8 km2 in 2020. The total area under vegetation was computed as 513.2 km2 in 2010 that increased to 601.6km2 in 2015 and further increased to 717.7 km2in 2020. Forest land use showed decreasing trend as the covered area in 2010 was occupied 90.8 km2 that decreased to 86.7 km2 in 2015 and further decreased to 61.84 km2 in 2020. In 2010, barren land use was occupied 528.54 km2 that considerably decreased to 429.64 km2 in 2015 further decreased to 333.1 km2 in 2020. Barren land drastically decreased into watered, built-up, and vegetation land uses. The findings of this study will be helpful for the future conservation of various land-use types, urban and regional planning, and an increase in agricultural production of various crops in the study area.

A Low-Sidelobe Circularly Polarized Continuous Beam-Scanning Array Using Double-Layer Rotated Structure for Ku-Band Satellite Communications

In this letter, a low-sidelobe level (SLL) circularly polarized (CP) beam-scanning array antenna based on a double-layer rotated structure is proposed for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ku</i> -band satellite communications. It is comprised of a 16 × 24 CP substrate integrated waveguide slot antenna array and a rotatable feeding network. Detailed design methodology and working mechanism of the proposed antenna array are presented and analyzed, in particular, the method of achieving low SLL in Blass matrix design. A prototype was fabricated and measured, and the measured results indicate that an AR < 1.5 dB and a max SLL suppression of 19.4 dB at 11.95 GHz can be achieved. Its superiorities of low profile, low SLL, high gain, and continuous beam-scanning ability make the proposed array antenna a promising candidate for satellite communications.

Classification comparison of Landsat-8 and Sentinel-2 data in Google Earth Engine, study case of the city of Kabul

In recent years, Kabul city's rapid urbanization has adversely affected the urban land cover, such as surface water bodies and croplands. Surface water resources are threatened due to overpopulation in the city either qualitatively or quantitatively, also croplands are being lost with the development of urbanization activities through the city. To monitor and assess surface changes accurately, we classified the city area using satellite images of both Landsat-8 and Sentinel-2 and compared both of their findings. The Support Vector Machine classifier was applied to multi-senor data to classify four different land categories using the same training sites and samples with the same period. All the procedures were conducted in Google Earth Engine (GEE) cloud platform. The surface reflectance bands of both satellites were used for classification. Confusion matrixes were created using the same reference points for Sentinel-2 and Landsat-8 classification to compare the results and determine the best approach for classification of land cover. Results show that overall accuracy was 94.26% for Sentinel-2 while it was 85.04% for Landsat-8, similarly, the Kappa coefficient was calculated 91.7% and 78.3% for Sentinel-2 and Landsat-8, respectively.