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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Engineering Remote Sensing".

Deadline for manuscript submissions: closed (31 July 2022) | Viewed by 18604

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Dr. Hugo Carreno-Luengo

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NASA CYGNSS Mission, Climate and Space Sciences and Engineering Department, University of Michigan, Ann Arbor, MI 48109, USA
Interests: GNSS-reflectometry; microwave radiometry; bistatic scattering; SmallSats; planetary sciences; water cycle; carbon cycle
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Dear Colleagues,

Advanced RF sensors and remote sensing instruments are key for the future advancement of Earth observation missions and instruments that include spin-off for planetary missions. Thanks to the development of systems and missions (formation flying, SmallSats, GNSS-reflectometry, ka-band SAR, InSAR, etc.), our community will be able to further understand the complex and dynamic processes taking place on the Earth’s surface and sub-surface, and all over the Earth’s atmosphere. The application of such techniques will enable one to make advances in geology, hydrology, glaciology, and oceanography. Accordingly, the development of novel technology (instrument front ends, digital beamforming, Cal/Val, on-board processing, atmospheric and ionospheric corrections, etc.) and sub-systems is encouraged.

This Special Issue aims to provide a review of instruments and state of the art in current and future mission concepts including applications, science objectives, mission design, and instrument technology. We expect to bring together and share the latest findings of experts from industry and research organizations involved in this research topic.

Dr. Hugo Carreno-Luengo
Guest Editor

Manuscript Submission Information

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Keywords

SmallSats
GNSS-reflectometry
ka-band altimetry
multi-channel SAR
planetary and space science

Published Papers (5 papers)

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Research

17 pages, 5395 KiB

Open AccessArticle

Performance Analysis of Ku/Ka Dual-Band SAR Altimeter from an Airborne Experiment over South China Sea

by Xiaonan Liu, Weiya Kong, Hanwei Sun and Yaobing Lu

Remote Sens. 2022, 14(10), 2362; https://0-doi-org.brum.beds.ac.uk/10.3390/rs14102362 - 13 May 2022

Cited by 3 | Viewed by 2065

Abstract

Satellite radar altimeters have been successfully used for sea surface height (SSH) measurement for decades, gaining great insight in oceanography, meteorology, marine geology, etc. To further improve the observation precision and spatial resolution, radar altimeters have evolved from real aperture to synthetic aperture, from the Ku-band to Ka-band. Future synthetic aperture radar (SAR) altimeter of the Ka-band is expected to achieve better performance than its predecessors. To verify the SAR altimeter data processing method and explore the system advantage of the Ka-band, a Ku/Ka dual-band SAR altimeter airborne experiment was carried out over South China Sea on 6 November 2021. Through dedicated hardware design, this campaign has acquired the Ku and Ka dual-band echo data simultaneously. The airborne data are processed to estimate the SSH retrieval precision after a series of procedures (including height compensation, range migration correction, multi-look processing, waveform re-tracking). To accustom to the airborne experiment design, a SAR echo model that fully considers both the attitude variation of the aircraft and the elliptical footprint of radar beam is established. The retrieved SSH data are compared with the public SSH data along the flight path at the experiment day, showing good consistence for both bands. By calculating the theoretical precision of waveform re-tracking and re-processing the dual-band airborne data into different bandwidths, it is demonstrated that the Ku/Ka precision ratio is possible to achieve 1.4 within the 27 km offshore area, which indicates that Ka-band has better performance. Full article

(This article belongs to the Special Issue Advanced RF Sensors and Remote Sensing Instruments)

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13 pages, 3845 KiB

Open AccessArticle

Cascaded Microwave Frequency Transfer over 300-km Fiber Link with Instability at the 10⁻¹⁸ Level

by Wenxiang Xue, Wenyu Zhao, Honglei Quan, Yan Xing and Shougang Zhang

Remote Sens. 2021, 13(11), 2182; https://0-doi-org.brum.beds.ac.uk/10.3390/rs13112182 - 03 Jun 2021

Cited by 9 | Viewed by 2994

Abstract

Comparing and synchronizing atomic clocks between distant laboratories with ultra-stable frequency transfer are essential procedures in many fields of fundamental and applied science. Existing conventional methods for frequency transfer based on satellite links, however, are insufficient for the requirements of many applications. In order to achieve high-precision microwave frequency transfer over a thousand kilometers of fiber and to construct a fiber-based microwave transfer network, we propose a cascaded system for microwave frequency transfer consisting of three 100-km single-span spooled fiber links using an improved electronic phase compensation scheme. The transfer instability measured for the microwave signal reaches 1.1 × 10⁻¹⁴ at 1 s and 6.8 × 10⁻¹⁸ at 10⁵ s, which agrees with the root-sum-square of each span contribution. It is feasible to extend the length of the fiber-based microwave frequency transfer up to 1200 km using 4 stages of our cascaded system, which is still sufficient to transfer modern cold atom microwave frequency standards. Moreover, the transfer instability of 9.0 × 10⁻¹⁵ at 1 s and 9.0 × 10⁻¹⁸ at 10⁵ s for a 100-MHz signal is achieved. The residual phase noise power spectral density of the 300-km cascaded link measured at 100-MHz is also obtained. The rejection frequency bandwidth of the cascaded link is limited by the propagation delay of one single-span link. Full article

(This article belongs to the Special Issue Advanced RF Sensors and Remote Sensing Instruments)

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Graphical abstract

19 pages, 7122 KiB

Open AccessArticle

Ocean Surface Topography Altimetry by Large Baseline Cross-Interferometry from Satellite Formation

by Weiya Kong, Bo Liu, Xiaohong Sui, Running Zhang and Jinping Sun

Remote Sens. 2020, 12(21), 3519; https://0-doi-org.brum.beds.ac.uk/10.3390/rs12213519 - 27 Oct 2020

Cited by 4 | Viewed by 1826

Abstract

Imaging Radar Altimeter (IRA) is the current development tendency for ocean surface topography (OST) altimetry, which utilizes Synthetic Aperture Radar (SAR) and interferometry to improve the spatial resolution of OST to several kilometers or even better. Meanwhile, centimetric altimetry accuracy should be guaranteed for applications such as geostrophic currents or marine gravity anomaly inversion. However, the baseline length of IRA which determines the altimetric sensitivity is confined by the satellite platform, in consideration of baseline vibration and payload capability. Therefore, the baseline length from a single satellite can extend to only tens of meters, making it difficult to achieve centimetric accuracy. Referring to the successful experience from TerraSAR-X/TanDEM-X, satellite formation can easily extend the baseline length to hundreds or thousands of meters, depending on the helix orbit. Therefore, we propose the large baseline IRA (LB-IRA) from satellite formation for OST altimetry: the carrier frequency shift (CFS) is brought in to compensate for the severe baseline decorrelation, and the helix orbit is carefully selected to prevent severe time decorrelation from along-track baseline. The numerical results indicate that the LB-IRA, whose cross-track baseline ranges between 629~1000 m and along-tack baseline ranges between 0~40 m, can achieve ~1 cm relative accuracy at 1 km resolution. Full article

(This article belongs to the Special Issue Advanced RF Sensors and Remote Sensing Instruments)

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Graphical abstract

15 pages, 5545 KiB

Open AccessArticle

Portable L-Band Radiometer (PoLRa): Design and Characterization

by Derek Houtz, Reza Naderpour and Mike Schwank

Remote Sens. 2020, 12(17), 2780; https://0-doi-org.brum.beds.ac.uk/10.3390/rs12172780 - 27 Aug 2020

Cited by 11 | Viewed by 6009

Abstract

A low-mass and low-volume dual-polarization L-band radiometer is introduced that has applications for ground-based remote sensing or unmanned aerial vehicle (UAV)-based mapping. With prominent use aboard the ESA Soil Moisture and Ocean Salinity (SMOS) and NASA Soil Moisture Active Passive (SMAP) satellites, L-band radiometry can be used to retrieve environmental parameters, including soil moisture, sea surface salinity, snow liquid water content, snow density, vegetation optical depth, etc. The design and testing of the air-gapped patch array antenna is introduced and is shown to provide a 3-dB full power beamwidth of 37°. We present the radio-frequency (RF) front end design, which uses direct detection architecture and a square-law power detector. Calibration is performed using two internal references, including a matched resistive source (RS) at ambient temperature and an active cold source (ACS). The radio-frequency (RF) front end does not require temperature stabilization, due to characterization of the ACS noise temperature by sky measurements. The ACS characterization procedure is presented. The noise equivalent delta (Δ) temperature (NEΔT) of the radiometer is ~0.14 K at 1 s integration time. The total antenna temperature uncertainty ranges from 0.6 to 1.5 K. Full article

(This article belongs to the Special Issue Advanced RF Sensors and Remote Sensing Instruments)

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29 pages, 9267 KiB

Open AccessArticle

Above-Ground Biomass Retrieval over Tropical Forests: A Novel GNSS-R Approach with CyGNSS

by Hugo Carreno-Luengo, Guido Luzi and Michele Crosetto

Remote Sens. 2020, 12(9), 1368; https://0-doi-org.brum.beds.ac.uk/10.3390/rs12091368 - 26 Apr 2020

Cited by 67 | Viewed by 4118

Abstract

An assessment of the National Aeronautics and Space Administration NASA’s Cyclone Global Navigation Satellite System (CyGNSS) mission for biomass studies is presented in this work on rain, coniferous, dry, and moist tropical forests. The main objective is to investigate the capability of Global Navigation Satellite Systems Reflectometry (GNSS-R) for biomass retrieval over dense forest canopies from a space-borne platform. The potential advantage of CyGNSS, as compared to monostatic Synthetic Aperture Radar (SAR) missions, relies on the increasing signal attenuation by the vegetation cover, which gradually reduces the coherent scattering component

σ^{coh, 0}

. This term can only be collected in a bistatic radar geometry. This point motivates the study of the relationship between several observables derived from Delay Doppler Maps (DDMs) with Above-Ground Biomass (AGB). This assessment is performed at different elevation angles

θ_{e}

as a function of Canopy Height (CH). The selected biomass products are obtained from data collected by the Geoscience Laser Altimeter System (GLAS) instrument on-board the Ice, Cloud, and land Elevation Satellite (ICESat-1). An analysis based on the first derivative of the experimentally derived polynomial fitting functions shows that the sensitivity requirements of the Trailing Edge

TE

and the reflectivity

Γ

reduce with increasing biomass up to ~ 350 and ~ 250 ton/ha over the Congo and Amazon rainforests, respectively. The empirical relationship between

TE

and

Γ

with AGB is further evaluated at optimum angular ranges using Soil Moisture Active Passive (SMAP)-derived Vegetation Optical Depth (

VOD

), and the Polarization Index (

PI

). Additionally, the potential influence of Soil Moisture Content (SMC) is investigated over forests with low AGB. Full article

(This article belongs to the Special Issue Advanced RF Sensors and Remote Sensing Instruments)

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