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A special issue of Remote Sensing (ISSN 2072-4292).

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 34808

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Dr. Isaac Ramos

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Guest Editor

Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Interests: RF design; real and synthetic aperture microwave radiometer; remote sensing; CubeSats
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Adriano Camps

E-Mail Website1 Website2
Co-Guest Editor

CommSensLab – UPC, “María de Maeztu” Excellence Research Unit, Dept. of Signal Theory and Communications, Universitat Politècnica de Catalunya—BarcelonaTech (UPC) and Institut d’Estudis Espacials de Catalunya IEEC/CTE-UPC. UPC Campus Nord, building D4, office 016, c/Jordi Girona 31, 08034 Barcelona, Spain
Interests: microwave radiometry; GNSS-R; RFI mitigation; CubeSats; SMOS; soil moisture; sea surface salinty
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Remote sensors have enabled a better understanding of the Earth’s climate and the interactions between the ocean, land, and atmosphere, improving the knowledge on the global Earth dynamics. During the last several decades, technology has experienced incredible developments, both in sensor design and data processing techniques. At present, miniaturization, increased communications and networking capabilities, as well as machine learning and artificial intelligence are enabling new remote sensing instrument concepts, including distributed and reconfigurable sensors, for satellite, airborne, and ground-based platforms. These new remote sensing technologies can potentially explore widespread fields, including but not limited to passive/active and microwave or millimeter-wave/optical, or a combination of those.

We invite authors to submit their work on remote sensing technology developments on any of the above fields. Technology advancements include any development at subsystem level, at a system (instrument) level, mission level, or even at system of systems level. We also encourage studies including the analysis of performance improvement in terms of spatial, radiometric, spectral or temporal resolutions, related to the scientific applications.

Dr. Isaac Ramos
Prof. Dr. Adriano Camps
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Remote sensing instruments
Active/passive RF sensors
Active/passive optical sensors
Reconfigurable, smart, and/or distributed remote sensors
CubeSat

Published Papers (12 papers)

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Research

22 pages, 5498 KiB

Open AccessArticle

RFI Detection and Mitigation for Advanced Correlators in Interferometric Radiometers

by Adrian Perez-Portero, Jorge Querol, Adriano Camps, Manuel Martin-Neira, Martin Suess, Juan Ignacio Ramirez, Alberto Zurita, Josep Closa, Roger Oliva and Raul Onrubia

Remote Sens. 2022, 14(18), 4672; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14184672 - 19 Sep 2022

Cited by 2 | Viewed by 1864

Abstract

This work presents the first RFI detection and mitigation algorithm for the interferometric radiometers that will be implemented in its correlator unit. The algorithm operates in the time and frequency domains, applying polarimetric and statistical tests in both domains, and exhibiting a tunable and arbitrary low probability of false alarm. It is scalable to a configurable number of receivers, and it is optimized in terms of quantization bits and the implementation of the cross-correlations in the time or frequency domains for hardware resource saving. New features of this algorithm are the computation of the Stokes parameters per frequency bin in the Short-Time Fourier Transform and a new parameter called Polarimetric Kurtosis. If RFI is detected in one domain or in both, it is removed using the calculated blanking masks. The optimum algorithm parameters are computed, such as length of the FFTs, the threshold selection for a given probability of false alarm, and the selection of the blanking masks. Last, an important result refers to the application of Parseval’s theorem for the computation of the cross-correlations in the frequency domain, instead of in the time domain, which is more efficient and leads to smaller errors even when using moderate quantization levels. The algorithm has been developed in the framework of the ESA’s technology preparation for a potential L-band radiometer mission beyond SMOS. However, it is also applicable to (polarimetric) real aperture radiometers, and its performance would improve if more than one bit is used in the signal quantization. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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24 pages, 3501 KiB

Open AccessEditor’s ChoiceArticle

SARCASTIC v2.0—High-Performance SAR Simulation for Next-Generation ATR Systems

by Michael Woollard, David Blacknell, Hugh Griffiths and Matthew A. Ritchie

Remote Sens. 2022, 14(11), 2561; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14112561 - 27 May 2022

Cited by 6 | Viewed by 3972

Abstract

Synthetic aperture radar has been a mainstay of the remote sensing field for many years, with a wide range of applications across both civilian and military contexts. However, the lack of openly available datasets of comparable size and quality to those available for optical imagery has severely hampered work on open problems such as automatic target recognition, image understanding and inverse modelling. This paper presents a simulation and analysis framework based on the upgraded SARCASTIC v2.0 engine, along with a selection of case studies demonstrating its application to well-known and novel problems. In particular, we demonstrate that SARCASTIC v2.0 is capable of supporting complex phase-dependent processing such as interferometric height extraction whilst maintaining near-realtime performance on complex scenes. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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26 pages, 16070 KiB

Open AccessArticle

Polarimetric Persistent Scatterer Interferometry for Ground Deformation Monitoring with VV-VH Sentinel-1 Data

by Feng Zhao, Teng Wang, Leixin Zhang, Han Feng, Shiyong Yan, Hongdong Fan, Dongbiao Xu and Yunjia Wang

Remote Sens. 2022, 14(2), 309; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14020309 - 10 Jan 2022

Cited by 10 | Viewed by 2708

Abstract

With the launch of the Sentinel-1 satellites, it becomes easy to obtain long time-series dual-pol (i.e., VV and VH channels) SAR images over most areas of the world. By combining the information from both VV and VH channels, the polarimetric persistent scatterer interferometry (PolPSI) techniques is supposed to achieve better ground deformation monitoring results than conventional PSI techniques (using only VV channel) with Sentinel-1 data. According to the quality metric used for polarimetric optimizations, the most commonly used PolPSI techniques can be categorized into three main categories. They are PolPSI-ADI (amplitude dispersion index as the phase quality metric), PolPSI-COH (coherence as the phase quality metric), and PolPSI-AOS (taking adaptive optimization strategies). Different categories of PolPSI techniques are suitable for different study areas and with different performances. However, the study that simultaneously applies all the three types of PolPSI techniques on Sentinel-1 PolSAR images is rare. Moreover, there has been little discussion about different characteristics of the three types of PolPSI techniques and how to use them with Sentinel-1 data. To this end, in this study, three data sets in China have been used to evaluate the three types of PolPSI techniques’ performances. Based on results obtained, the different characteristics of PolPSI techniques have been discussed. The results show that all three PolPSI techniques can improve the phase quality of interferograms. Thus, more qualified pixels can be used for ground deformation estimation by PolPSI methods with respect to the PSI technique. Specifically, this pixel density improvement is 50%, 12%, and 348% for the PolPSI-ADI, PolPSI-COH, and POlPSI-AOS, respectively. PolPSI-ADI is the most efficient method, and it is the first choice for the area with abundant deterministic scatterers (e.g., urban areas). Benefitting from its adaptive optimization strategy, PolPSI-AOS has the best performances at the price of highest computation cost, which is suitable for rural area applications. On the other hand, limited by the medium resolution of Sentinel-1 PolSAR images, PolPSI-COH’s improvement with respect to conventional PSI is relatively insignificant. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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20 pages, 4499 KiB

Open AccessArticle

The Effect of Spatial Resolution and Temporal Sampling Schemes on the Measurement Error for a Moon-Based Earth Radiation Observatory

by Wentao Duan, Jiandong Liu, Qingyun Yan, Haibing Ruan and Shuanggen Jin

Remote Sens. 2021, 13(21), 4432; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13214432 - 03 Nov 2021

Cited by 2 | Viewed by 2154

Abstract

The Moon-Based Earth Radiation Observatory (MERO) is a new platform, which is expected to advance current Earth radiation budget (ERB) research with better observations. For the instrument design of a MERO system, ascertaining the spatial resolution and sampling scheme is important. However, current knowledge about this is still limited. Here we proposed a simulation method for the MERO-measured Earth top of atmosphere (TOA) outgoing shortwave radiation (OSR) and outgoing longwave radiation (OLR) fluxes and constructed the “true” Earth TOA OSR and OLR fluxes based on the Clouds and Earth’s Radiant Energy System (CERES) data. Then we used them to reveal the effects of spatial resolution and temporal scheme (sampling interval and the temporal sampling sequence) on the measurement error of a MERO. Our results indicate that the spatial sampling error in the unit of percentage reduces linearly as the spatial resolution varies from 1000 km to 100 km; the rate is 2.5%/100 km for the Earth TOA OSR flux, which is higher than that (1%/100 km) of the TOA OLR flux. Besides, this rate becomes larger when the spatial resolution is finer than 40 km. It is also demonstrated that a sampling temporal sequence of starting time of 64 min with a sampling interval of 90 min is the optimal sampling scheme that results in the least temporal sampling error for the MERO system with a 40 km spatial resolution, note that this conclusion depends on the temporal resolution and quality of the data used to construct the “true” Earth TOA OSR and OLR fluxes. The proposed method and derived results in this study could facilitate the ascertainment of the optimal spatial resolution and sampling scheme of a MERO system under certain manufacturing budget and measurement error limit. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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14 pages, 3635 KiB

Open AccessCommunication

Prediction of Target Detection Probability Based on Air-to-Air Long-Range Scenarios in Anomalous Atmospheric Environments

by Tae-Heung Lim and Hosung Choo

Remote Sens. 2021, 13(19), 3943; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13193943 - 02 Oct 2021

Cited by 4 | Viewed by 1973

Abstract

We investigate a target detection probability (TDP) using path loss of an airborne radar based on air-to-air scenarios in anomalous atmospheric and weather environments. In the process of calculating the TDP, it is necessary to obtain the overall path loss including the anomalous atmospheric environment, gas attenuation, rainfall attenuation, and beam scanning loss. The path loss including the quad-linear refractivity model and other radar input parameters is simulated using the Advanced Refractive Effects Prediction System (AREPS) software along the range and the altitude. For the gas and rainfall attenuations, ITU-R models are used to consider the weather environment. In addition, the radar beam scan loss and a radar cross section (RCS) of the target are considered to estimate the TDP of the airborne long-range radar. The TDP performance is examined by employing the threshold evaluations of the total path loss derived from the detectability factor and the free-space radar range equation. Finally, the TDPs are obtained by assuming various air-to-air scenarios for the airborne radar in anomalous atmospheric and weather environments. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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18 pages, 4402 KiB

Open AccessArticle

A Time-Domain Simulation System of MICAP L-Band Radiometer for Pre-Launch RFI Processing Study

by Tianshu Guo, Xi Guo, Cheng Zhang, Donghao Han, Lijie Niu, Hao Liu and Ji Wu

Remote Sens. 2021, 13(16), 3230; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13163230 - 14 Aug 2021

Cited by 3 | Viewed by 1892

Abstract

Microwave Imager Combined Active and Passive (MICAP), which is a package of active and passive microwave instruments including L/C/K-band radiometers and L-band scatterometer, has been approved to be taken onbord the Chinese Ocean Salinity Mission. The L-band one-dimensional synthetic aperture radiometer (L-Rad) is the key part of MICAP to measure sea surface salinity (SSS). Since radio frequency interference (RFI) is reported as a serious threat to L-band radiometry, the RFI detection and mitigation techniques must be carefully designed before launch. However, these techniques need to be developed based on the knowledge of how RFI affects complex correlation, visibility function, and reconstructed brightness temperature. This paper presents a time-domain signal modeling method for the simulation of interferometric measurement under RFI’s presences, and a simulation system for L-Rad is established accordingly. Several RFI cases are simulated with different RFI types, parameters, and positions; and the RFI characteristics upon L-Rad’s measurement are discussed. The proposed simulation system will be further dedicated to the design of RFI processing strategy onboard MICAP. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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18 pages, 98707 KiB

Open AccessArticle

Analysis of Groundwater Depletion/Inflation and Freeze–Thaw Cycles in the Northern Urumqi Region with the SBAS Technique and an Adjusted Network of Interferograms

by Baohang Wang, Qin Zhang, Antonio Pepe, Pietro Mastro, Chaoying Zhao, Zhong Lu, Wu Zhu, Chengsheng Yang and Jing Zhang

Remote Sens. 2021, 13(11), 2144; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13112144 - 29 May 2021

Cited by 6 | Viewed by 2253

Abstract

This work investigated the large-scale ground deformations threatening the Northern Urumqi district, China, which are connected to groundwater exploitation and the seasonal freeze–thaw cycles that characterize this frozen region. Ground deformations can be well captured by satellite data using a multi-temporal interferometric synthetic aperture radar (Mt-InSAR) approach. The accuracy of the achievable ground deformation products (e.g., mean displacement time series and related ground displacement time series) critically depends on the number and quality of the selected interferograms. This paper presents a straightforward interferogram selection algorithm that can be applied to identify an optimal network of small baseline (SB) interferograms. The selected SB interferograms are then used to produce ground deformation products using the well-known small baseline subset (SBAS) Mt-InSAR algorithm. The developed interferogram selection algorithm (ISA) permits the selection of the group of SB data pairs that minimize the relative error of the mean ground deformation velocity. Experiments were carried out using a group of 102 Sentinel-1B SAR data collected from 12 April 2017 to 29 October 2020. This research study shows that the investigated farmland region is characterized by a maximum ground deformation rate of about 120 mm/year. Periodic groundwater overexploitation, coupled with irrigation and freeze–thaw phases, is also responsible for seasonal (one-year) ground displacement signals, with oscillation amplitudes up to 120 mm in the zones of maximum displacement. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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17 pages, 4465 KiB

Open AccessArticle

Calibration of a Polarimetric Microwave Radiometer Using a Double Directional Coupler

by Luisa de la Fuente, Beatriz Aja, Enrique Villa and Eduardo Artal

Remote Sens. 2021, 13(11), 2109; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13112109 - 27 May 2021

Cited by 3 | Viewed by 1753

Abstract

This paper presents a built-in calibration procedure of a 10-to-20 GHz polarimeter aimed at measuring the I, Q, U Stokes parameters of cosmic microwave background (CMB) radiation. A full-band square waveguide double directional coupler, mounted in the antenna-feed system, is used to inject differently polarized reference waves. A brief description of the polarimetric microwave radiometer and the system calibration injector is also reported. A fully polarimetric calibration is also possible using the designed double directional coupler, although the presented calibration method in this paper is proposed to obtain three of the four Stokes parameters with the introduced microwave receiver, since V parameter is expected to be zero for the CMB radiation. Experimental results are presented for linearly polarized input waves in order to validate the built-in calibration system. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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17 pages, 11153 KiB

Open AccessArticle

The Penetration Analysis of Airborne Ku-Band Radar Versus Satellite Infrared Lidar Based on the Height and Energy Percentiles in the Boreal Forest

by Hui Zhou, Yuwei Chen, Teemu Hakala, Ziyi Feng, Changhui Jiang, Jianxin Jia, Haibin Sun and Juha Hyyppä

Remote Sens. 2021, 13(9), 1650; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13091650 - 23 Apr 2021

Viewed by 3153

Abstract

The paper investigates the penetration properties of an airborne Ku-band frequency modulated continuous waveform (FMCW) profiling radar named Tomoradar and a satellite near-infrared lidar into the boreal forest of Finland. We achieve the accumulative energy distributions based on the Tomoradar waveforms and the satellite lidar waveforms generated from the high-density airborne lidar data within Tomoradar footprints. By comparing two groups of the height percentiles and energy percentiles derived from the accumulative energy distributions, we evaluate the relationship of penetrations between the Ku-band microwave and near-infrared laser according to the coefficients of the determination (COD), and the root mean square errors (RMSE) of linear regression analyses. The quantitative analysis results demonstrate that the height and energy percentiles derived from Tomoradar waveforms correlate well with those from satellite lidar waveforms with the mean correlation coefficients of more than 0.78 and 0.85. The linear regression models for the height and energy percentile produce excellent fits with the mean CODs of 0.95 and 0.90 and the mean RMSEs of 1.25 m and 0.03, respectively. Less than 15% of height percentiles and 87.54% of the energy percentiles in the sixth stratum near the ground derived from Tomoradar waveforms surpass those from satellite lidar waveforms. Hence, the Ku-band microwave can penetrate deeper into the forest than the near-infrared laser at the same spatial scale. In addition, quadratic fitting models are established to describe the differences of the height percentile (DHP) and the energy percentile (DEP) to expound the canopy height and closure contributions numerically. The facts that the CODs of the DHP and DEP individually are more than 0.96 and 0.89 and the fitting residual histograms approximate to normal distributions reveal the reliabilities of the proposed fitting models. Thus, the penetration analyses are valid for the explorations on the FMCW radar applications and the data fusion of the Ku-band radar and near-infrared lidar in the forest investigations. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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19 pages, 18235 KiB

Open AccessArticle

A Multi-Frequency SDR-Based GBSAR: System Overview and First Results

by Adrià Amézaga, Carlos López-Martínez and Roger Jové

Remote Sens. 2021, 13(9), 1613; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13091613 - 21 Apr 2021

Cited by 1 | Viewed by 3280

Abstract

This work describes a system-level overview of a multi-frequency GBSAR built around a high performance software defined radio (SDR). The main goal of the instrument is to be employed as a demonstrator and experimental platform for multi-frequency GBSAR campaigns. The system is capable of operating in P, L, C and X-bands, and signal generation and digital signal processing are customizable and reconfigurable through software. An overview of the software and hardware and implementations of the system are presented. The operation of the system is demonstrated with two measuring campaigns showing focused amplitude images at different frequencies. It is shown how the usage of SDR for GBSAR systems is a viable design option. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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20 pages, 8230 KiB

Open AccessArticle

Sequential 90° Rotation of Dual-Polarized Antenna Elements in Linear Phased Arrays with Improved Cross-Polarization Level for Airborne Synthetic Aperture Radar Applications

by Diego Lorente, Markus Limbach, Bernd Gabler, Héctor Esteban and Vicente E. Boria

Remote Sens. 2021, 13(8), 1430; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13081430 - 08 Apr 2021

Cited by 4 | Viewed by 3123

Abstract

In this work, a novel rotation approach for the antenna elements of a linear phased array is presented. The proposed method improves by up to 14 dB the cross-polarization level within the main beam by performing a sequential 90° rotation of the identical array elements, and achieving measured cross-polarization suppressions of 40 dB. This configuration is validated by means of simulation and measurements of a manufactured linear array of five dual-polarized cavity-box aperture coupled stacked patch antennas operating in L-Band, and considering both uniform amplitude and phase distribution and beamforming with amplitude tapering. The analysis is further extended by applying and comparing the proposed design with the 180° rotation and non-rotation topologies. This technique is expected to be used for the next generation L-Band Airborne Synthetic Aperture Radar Sensor of the German Aerospace Center (DLR). Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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19 pages, 5749 KiB

Open AccessArticle

In-Orbit Validation of the FMPL-2 Instrument—The GNSS-R and L-Band Microwave Radiometer Payload of the FSSCat Mission

by Joan Francesc Munoz-Martin, Lara Fernandez, Adrian Perez, Joan Adrià Ruiz-de-Azua, Hyuk Park, Adriano Camps, Bernardo Carnicero Domínguez and Massimiliano Pastena

Remote Sens. 2021, 13(1), 121; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13010121 - 31 Dec 2020

Cited by 32 | Viewed by 3597

Abstract

The Flexible Microwave Payload-2 is the GNSS-R and L-band Microwave Radiometer Payload on board

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Cat-5/A, one of the two 6-unit CubeSats of the FSSCat mission, which were successfully launched on 3 September 2020 on Vega flight VV16. The instrument occupies nearly a [...] Read more.

The Flexible Microwave Payload-2 is the GNSS-R and L-band Microwave Radiometer Payload on board

^{3}

Cat-5/A, one of the two 6-unit CubeSats of the FSSCat mission, which were successfully launched on 3 September 2020 on Vega flight VV16. The instrument occupies nearly a single unit of the CubeSat, and its goal is to provide sea-ice extension and thickness over the poles, and soil moisture maps at low-moderate resolution over land, which will be downscaled using data from Cosine Hyperscout-2 on board

^{3}

Cat-5/B. The spacecrafts are in a 97.5

^{°}

inclination Sun-synchronous orbit, and both the reflectometer and the radiometer have been successfully executed and validated over both the North and the South poles. This manuscript presents the results and validation of the first data sets collected by the instrument during the first two months of the mission. The results of the validation are showing a radiometric accuracy better than 2 K, and a sensitivity lower than the Kelvin. For the reflectometer, the results are showing that the sea-ice transition can be estimated even at short integration times (40 ms). The presented results shows the potential for Earth Observation missions based on CubeSats, which temporal and spatial resolution can be further increased by means of CubeSat constellations. Full article

(This article belongs to the Special Issue New Technologies for Earth Remote Sensing)

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