Effect of the ingestion in the WRF model of different Sentinel-derived and GNSS-derived products: analysis of the forecasts of a high impact weather event

This paper presents the first experimental results of a study on the ingestion in the Weather Research and Forecasting (WRF) model, of Sentinel satellites and Global Navigation Satellite Systems (GNSS) derived products. The experiments concern a flash-floodevent occurred in Tuscany (Central Italy) in September 2017. The rationale is that numerical weather prediction (NWP) models are presently able to produce forecasts with a km scale spatial resolution, but the poor knowledge of the initial state of the atmosphere may imply an inaccurate simulation of the weather phenomena. Hence, to fully exploit the advances in numerical weather modelling, it is necessary to feed them with high spatiotemporal resolution information over the surface boundary and the atmospheric column. In this context, the Copernicus Sentinel satellites represent an important source of data, because they can provide a set of high-resolution observations of physical variables (e.g. soil moisture, land/sea surface temperature, wind speed) used in NWP models runs. The possible availability of a spatially dense network of GNSS stations is also exploited to assimilate water vapour content. Results show that the assimilation of Sentinel-1 derived wind field and GNSS-derivedwater vapour data produce the most positive effects on the performance of the forecast

SKIM, a candidate satellite mission exploring global ocean currents and waves

The Sea surface KInematics Multiscale monitoring (SKIM) satellite mission is designed to explore ocean surface current and waves. This includes tropical currents, notably the poorly known patterns of divergence and their impact on the ocean heat budget, and monitoring of the emerging Arctic up to 82.5°N. SKIM will also make unprecedented direct measurements of strong currents, from boundary currents to the Antarctic circumpolar current, and their interaction with ocean waves with expected impacts on air-sea fluxes and extreme waves. For the first time, SKIM will directly measure the ocean surface current vector from space. The main instrument on SKIM is a Ka-band conically scanning, multi-beam Doppler radar altimeter/wave scatterometer that includes a state-of-the-art nadir beam comparable to the Poseidon-4 instrument on Sentinel 6. The well proven Doppler pulse-pair technique will give a surface drift velocity representative of the top meter of the ocean, after subtracting a large wave-induced contribution. Horizontal velocity components will be obtained with an accuracy better than 7 cm/s for horizontal wavelengths larger than 80 km and time resolutions larger than 15 days, with a mean revisit time of 4 days for of 99% of the global oceans. This will provide unique and innovative measurements that will further our understanding of the transports in the upper ocean layer, permanently distributing heat, carbon, plankton, and plastics. SKIM will also benefit from co-located measurements of water vapor, rain rate, sea ice concentration, and wind vectors provided by the European operational satellite MetOp-SG(B), allowing many joint analyses. SKIM is one of the two candidate satellite missions under development for ESA Earth Explorer 9. The other candidate is the Far infrared Radiation Understanding and Monitoring (FORUM). The final selection will be announced by September 2019, for a launch in the coming decade

Large reflector antennas observed with space-based synthetic aperture radar

Recente observaties (2011) van grote reflector antennes op de grond met Synthetische Apertuur Radar (SAR) vanuit de ruimte worden besproken. Resultaten verzameld in het verleden met ERS worden aangegeven. De recentelijk gemeten resultaten worden aangegeven met suggesties om meer preciese resultaten te krijgen. Zulk soort van radar doelen kan uitermate interessant zijn voor SARs die opereren op lagere frekwenties zoal Biomass missie. Het zijn doelen die er toch al zijn en mede gebruikt kunnen worden om de operatie van de SAR in de gaten te houden. De response is stabeil en complex van aard (een radar cross sectie is een scalaire grootheid). Een voor de hand liggend doel, eigenlijk automatisch en zonder extra effort beschikbaar is het data grondstation voor zo'n SAR, meestal een antenne met een reflector met een diameter van zo'n ca 7 meter. Als dan de SAR satelliet data naar beneden stuurt en ook nog een SAR meting doet over het gebied met die antenne erin, dan verschijnt dat doel in the waarnemingen, dus in het SAR plaatje

Observation of radiotelescope RT22 CrAO with the synthetic aperture radar envisat from space

De radiotelescoop RT22 van de Crimean Radio Astronomy Observatory (CRAO) is geobserveerd met de synthetische apertuur radar op Envisat. Radars in de ruimte kunnen gebaat zijn met bepaalde radar targets met een sterke en systematische radar reflectie (radar cross section). Het betreft hier initiele onderzoekingen om te kijken of dit van nut kan zijn voor de BIOMASS radar missie. The RT22 CrAO radio telescope antenna has been observed with a C-band Synthetic Aperture Radar (SAR) for the purpose of deriving scattering properties and pointing information. Space-based radars benefit from accurate calibration targets and for the lower frequency bands such targets can be rather large in physical sense in order to derive level information. Active transponders are used. A large reflector antenna has a scattering pattern, which depends on a number of properties and compares with the actual radiation pattern of the antenna (minimum scattering antenna, depending on loading considerations). We have done preliminary investigations by measuring the responses with the SAR on-board ENVISAT

Time-Domain SAR Processor for Sentinel 1 TOPS Data

This paper presents a time-domain synthetic aperture radar (SAR) processor designed for Sentinel-1 Terrain Observation by Progressive Scans (TOPS) monostatic data. The processor focuses Interferometric Wide (IW) swath and Extra Wide (EW) swath data on a selected region-of-interest (ROI) and consists of the following main stages: decoding of Level-0 data, selection of the relevant burst and pulses for the targeted ROI, range compression, azimuth frequency unfolding and resampling, and image focusing by a fast subaperture-based version of the back-projection algorithm. The performances of the developed processor are assessed on datasets acquired in IW and EW imaging modes. Such a time-domain processor can be regarded as a first step towards a geometry/frequency-agnostic SAR processing kernel for future monostatic/multistatic spaceborne SAR missions

Ground-based reflector antennas observed with space-based synthetic aperture radar

Al eerder heeft deze auteur gerapporteerd over reflector antennes als doel voor synthetisch apertuur radar. Een aantal waarnemingen worden beschreven in deze paper, met verschillend resultaat. Heronder een raflector antenne op een gebouw vlak bij Estec, enkele grondstation antennes van ESA in Spanje (Villafranca) en een radio telescoop in de Krim. De resultaten zijn aanleiding om dit weer te bekijken voor de aardobservatie BIOMASS. Recent space-based Synthetic Aperture Radar (SAR) observations are discussed of large reflector antennas on the ground. The results are elaborated with suggestions for further work to arrive at more precise information. Such targets might eventually receive further attention in applications with SAR operating at lower frequency than for which the ground-station antenna operates. Being below cut-off, the antenna becomes a passive scattering structure with a Radar Cross Section (RCS). Such antenna may function as stable target of opportunity, additional to transponders. Its response should be stable (even in complex vectorial sense). Precise prediction requires accurate modelling. A target is automatically available (“free of charge”), when the low-frequency SAR instrument is switched on over the ground-station antenna for data downloading and when the latter antenna is located within the SAR image coverage

Multi-Aperture Focusing in Spaceborne Transmitter-Stationary Receiver Bistatic SAR

The paper proposes a methodology to perform azimuth focusing of spaceborne transmitter-stationary receiver bistatic synthetic aperture radar (SAR) data across multiple along-track apertures to increase azimuth resolution. The procedure uses as input several azimuth apertures (continuous groups of range compressed pulses) from one or more satellite bursts and comprises the following stages: azimuth antenna pattern compensation, slow time resampling, reconstruction of missing azimuth samples between neighbouring sets of pulses using an auto-regressive model and back-projection focusing of the resulting multi-aperture range image. The approach is evaluated with real bistatic data acquired over an area of Bucharest city, Romania

A Radargrammetric Approach for Spaceborne Transmitter-Stationary Receiver Bistatic SAR

This paper addresses the feasibility of exploiting a radargrammetric procedure for the retrieval of height estimates using stereo images acquired in a space-surface (spaceborne transmitter-stationary receiver) bistatic geometry. Currently, the research interest concerning this particular direction is still in its infancy, as there are very few papers partially covering the subject. The method proposed in this study is applied to a set of SAR images (displaying an urban area of the Bucharest city) in order to assess the elevation of a group of selected targets within the remotely sensed zone

Multiaperture Focusing for Spaceborne Transmitter/Ground-Based Receiver Bistatic SAR

The article proposes a methodology to perform azimuth focusing of spaceborne transmitter-stationary receiver bistatic synthetic aperture radar data across multiple along-track apertures to increase azimuth resolution. The procedure uses as input several azimuth apertures (continuous groups of range compressed pulses) from one or more satellite bursts and comprises the following stages: antenna pattern compensation, slow time resampling, reconstruction of missing azimuth samples between neighboring sets of pulses using an autoregressive (AR) model and back-projection focusing of the resulting multiaperture range image. A novel, highly efficient method is proposed to estimate the optimal order for the AR model. It differs from the traditional approach that uses the Akaike Information Criterion to directly estimate the order because the proposed method estimates the order indirectly by detecting the number of targets using principle component analysis. Spatial smoothing is used to obtain a full rank covariance matrix, whose eigenvalues are then analyzed using minimum description length. The optimal order is an integer multiple of the number of targets, which depends on signal-to-noise ratio. The approach is evaluated with real bistatic data acquired over an area of Bucharest city, Romania

Sentinel-1 InSAR Coherence as an Indicator of Monitor Farming Activities

Reliable crop monitoring is paramount to achieve the objectives of the Common Agricultural Policy (CAP) and Food and Agriculture Organization. Synthetic Aperture Radar (SAR) provides high-resolution imaging and all-weather data acquisition capabilities for crop monitoring. This study investigates the sensitivity of parcel-level Sentinel-1 interferometric coherence to farming activities (e.g. planting, emergence, harvest and tillage) and weather events. A methodology to detect activities was developed and validated using ground-truth data from four crop types, collected over four years. The proposed approach was able to detect over 60% of all nine different farming activities. The results show that interferometric coherence is a reliable indicator for farming activities that can be considered as events resulting in a clear structural change (e.g. tillage 100%), but less reliable for gradual changes (e.g. Emergence 40%).Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Mathematical Geodesy and Positionin