Copernicus Sentinel-1 satellites: sensitivity of antenna offset estimation to orbit and observation modelling

Peter, Heike; Fernández, Jaime; Féménias, Pierre

doi:10.5194/adgeo-50-87-2020

Cited by 15 publications

(6 citation statements)

References 19 publications

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“…The orbit ephemerides products of Sentinel‐1A and Sentinel‐1B changed on 29th and 30 July 2020, respectively, to version 1.7, incorporating a correction of the on‐board GPS antenna reference point position, as identified by Peter et al. (2020). This correction implied a 3‐D position change of approximately 60 mm and led to a decrease in the root mean square error (RMSE) of the 3‐D position of the satellites to below 10 mm (Peter et al., 2021a, 2021b).…”

Section: Effect Of Updated Orbit Ephemeridesmentioning

confidence: 99%

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

Lázecký

Hooper

Piromthong

2023

Geophysical Research Letters

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With the launch of the Copernicus Sentinel-1 Synthetic Aperture Radar (SAR) mission, the geoscience community acquired a unique tool for making precise measurements of large-scale surface deformation. The Center for Observation and Modeling of Earthquakes, Volcanoes and Tectonics (COMET) LiCSAR system (Lazecký et al., 2020) routinely generates Sentinel-1 differential interferograms over tectonic and volcanic areas, and carries out interferometric (InSAR) time series analyses to measure surface deformation in the satellite line-of-sight direction. When the satellites are traveling south to north (ascending), the look direction is downwards and slightly north of eastwards, and when moving north to south (descending) it is downwards and slightly north of westwards. The two geometries can therefore be used to accurately constrain the vertical and east-west components of any motion, but the line-of-sight sensitivity is very low for the north-south component, which is typically estimated using available GNSS data (Weiss et al., 2020).It is possible to estimate along-track displacements, which are sensitive to northward motions, by exploiting spectral diversity in the along-track, or azimuth, direction (Bechor & Zebker, 2006). This involves forming two sub-apertures for each SAR image, one with a look direction pointing slightly forwards and one pointing slightly backwards. Differencing interferograms formed from the forward-looking images and backward-looking images, results in phase change due to along-track displacement only, as displacement perpendicular to the flight direction cancels. The precision of these measurements is poor, however, as the difference in angle between the two sub-apertures is very small, particularly for the Interferometric Wideswath mode of Sentinel-1, which is the standard mode over land, due to the reduced Doppler spectrum available for each subswath.

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Section: Effect Of Updated Orbit Ephemeridesmentioning

confidence: 99%

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

Lázecký

Hooper

Piromthong

2023

Geophysical Research Letters

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“…The above self-shadowing algorithm was implemented into the Bernese GNSS Software and used for POD tests of the Copernicus Sentinel-1A satellite (about 700 km altitude). The "standard" Sentinel-1 macro model (proposed by the Copernicus POD Service) consists of 8 flat plates, modeling the satellite bus, SAR antenna and solar panels (Peter et al, 2020). For the present study, a 14-plate macro model with separate plates for the bus −z plate, the two back sides of the SAR antenna, separate plates for the front and back solar panels, and the long SAR antenna side plates is used.…”

Section: Initializationmentioning

confidence: 99%

Simple self-shadowing in precise orbit determination of Copernicus Sentinel satellites

Arnold¹,

Peter²,

Jäggi³

2023

Preprint

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Numerous non-gravitational accelerations (NGAs) &#8211; due to radiation or gas-surface interactions &#8211; act on a typical satellite in low Earth orbit. The modeling of these accelerations is a key aspect of (reduced-)dynamic satellite precise orbit determination. Opposed to a purely empirical estimation of NGAs, especially orbit solutions with a high dynamical stiffness require an explicit NGA forward modelling. This is most important, e.g., for altimetry satellites which require utmost orbit accuracy especially in radial direction. For explicit NGA modelling, a commonly employed strategy is to describe the satellite body in terms of a relatively simple macro model, i.e., a geometry composed of a number of elementary shapes like flat plates, spheres or cylinders, each of which with a specific size, orientation and surface property. During orbit integration, for each individual elementary surface NGAs are then computed based on analytical expressions and the sum over all surfaces yields the total NGA of the satellite at integration epoch. Often each of the elementary surface of the satellite macro model is treated fully independent from the other surfaces and interactions, in particular the (partial) occultation or shadowing of one surface by other surfaces is neglected. In case of satellites with significant non-convex shapes (like the altimetry satellite Sentinel-6A) this can lead to a marked degradation of NGA modeling. On the other hand, very detailed satellite geometry models together with techniques like ray tracing can provide highly accurate NGAs, however, at the price of significantly increased processing times. In this contribution we assess the performance of a relatively simple self-shadowing algorithm for satellites described by a collection of flat convex polygons. Based on the relative plate locations, for each plate we analytically determine the amount of shadow cast by the other plates. We quantify the cost in terms of processing time and the impact on dynamic orbit solutions for the Copernicus Sentinel satellites in terms of empirical orbit parameters, observation residuals as well as other orbit quality metrics. We compare the so-derived NGAs and orbit solutions to results obtained with different other macro models and alternative approaches to take self-shadowing into account.

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“…Removal of these nontectonic deformations depends on the established models instead of a simple linear fitting [62][63][64]. Additionally, given that the GPS antenna reference point (ARP) of Copernicus Sentinel-1 Precise Orbit Determination has changed at the end of July 2020 (S1A:29/07/2020, S1B:30/07/2020) [65], this ARP correction directly introduces the orbital position change. 3D position change can reach almost 6 cm for some regions [24].…”

Section: A Some Insights Into Azimuth Misregistration Correctionmentioning

confidence: 99%

Challenges and Prospects to Time Series Burst Overlap Interferometry (BOI): Some Insights From a New BOI Algorithm Test Over the Chaman Fault

Wei

et al. 2022

IEEE Trans. Geosci. Remote Sensing

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How to obtain millimeter-scale along-track deformations using phase measurements is still a pending question for InSAR community. Although Burst Overlap Interferometry (BOI) technique makes this question seem tractable, most applications of BOI still focus on extracting centimeter-scale deformations for co-seismic cases. To further improve measurement accuracy, here we propose a new time series BOI algorithm towards maximizing the performance of BOI and obtaining as high accuracy of the along-track deformations as possible. This algorithm has three major steps. The first step is to enhance BOI phase signal-to-noise ratio using our newly proposed phase estimator. In the second step, we apply a strain model-based method to further suppress the phase noise and rescue more data points. In the third step, a misregistration correction procedure which considers plate motion is applied to mitigate BOI time series bias. We tested our proposed algorithm over the Chaman fault. Although the derived millimeter-scale deformations demonstrate the effectiveness of our method, experimental results show that decorrelation and ionospheric disturbance are still two great challenges of BOI techniques.

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Copernicus Sentinel-1 satellites: sensitivity of antenna offset estimation to orbit and observation modelling

Cited by 15 publications

References 19 publications

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

Simple self-shadowing in precise orbit determination of Copernicus Sentinel satellites

Challenges and Prospects to Time Series Burst Overlap Interferometry (BOI): Some Insights From a New BOI Algorithm Test Over the Chaman Fault

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