Satellite Altimetry: Principles and Applications in Earth Sciences

Frappart, Frédéric; Blumstein, Denis; Cazenave, Anny; Ramillien, Guillaume; Birol, Florence; Morrow, Rosemary; Rémy, Frédérique

doi:10.1002/047134608x.w1125.pub2

Cited by 15 publications

(20 citation statements)

References 165 publications

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“…The satellite altitude (H) referred to an ellipsoid is also accurately known from orbitography modeling. Taking into account propagation delays due to interactions of electromagnetic wave in the atmosphere and geophysical corrections, the height of the reflecting surface (h) with reference to an ellipsoid or a geoid can be estimated as [16,17]:…”

Section: Altimetry Data Processingmentioning

confidence: 99%

Monitoring Sea Level and Topography of Coastal Lagoons Using Satellite Radar Altimetry: The Example of the Arcachon Bay in the Bay of Biscay

et al. 2018

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Radar altimetry was initially designed to measure the marine geoid. Thanks to the improvement in the orbit determination from the meter to the centimeter level, this technique has been providing accurate measurements of the sea surface topography over the open ocean since the launch of Topex/Poseidon in 1992. In spite of a decrease in the performance over land and coastal areas, it is now commonly used over these surfaces. This study presents a semi-automatic method that allows us to discriminate between acquisitions performed at high tides and low tides. The performances of four radar altimetry missions (ERS-2, ENVISAT, SARAL, and CryoSat-2) were analyzed for the retrieval of sea surface height and, for the very first time, of the intertidal zone topography in a coastal lagoon. The study area is the Arcachon Bay located in the Bay of Biscay. The sea level variability of the Arcachon Bay is characterized by a standard deviation of 1.05 m for the records used in this study (2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017). Sea surface heights are very well retrieved for SARAL (R~0.99 and RMSE < 0.23 m) and CryoSat-2 (R > 0.93 and RMSE < 0.42 m) missions but also for ENVISAT (R > 0.82 but with a higher RMSE >0.92 m). For the topography of the intertidal zone, very good estimates were also obtained using SARAL (R~0.71) and CryoSat-2 (R~0.79) with RMSE lower than 0.44 m for both missions.

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Section: Altimetry Data Processingmentioning

confidence: 99%

Monitoring Sea Level and Topography of Coastal Lagoons Using Satellite Radar Altimetry: The Example of the Arcachon Bay in the Bay of Biscay

et al. 2018

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“…A negative bias indicates that the measure of the SSH by the altimeter is underestimated; either the altimeter range is being overestimated, or the orbit is biased downwards [6]. The SSH from the altimeter is given as [2,37]:…”

Section: Ssh From Altimetrymentioning

confidence: 99%

“…Satellite altimetry is a radar technique detailing the topography of the earth's surface based on the measurement of the distance between the satellite and the surface, derived from the two-way travel time of an electromagnetic wave emitted by the altimeter, or altimeter range and the precise knowledge of the satellite orbit [1,2]. The primary objectives of satellite radar altimetry are to measure the marine geoid, ocean currents, and sea level variability.…”

Section: Introductionmentioning

confidence: 99%

Multi-Satellite Altimeter Validation along the French Atlantic Coast in the Southern Bay of Biscay from ERS-2 to SARAL

Frappart

Darrozes

et al. 2018

Remote Sensing

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Monitoring changes in coastal sea levels is necessary given the impacts of climate change. Information on the sea level and its changes are important parameters in connection to climate change processes. In this study, radar altimetry data from successive satellite missions, European Remote Sensing-2 (ERS-2), Jason-1, Envisat, Jason-2, and Satellite with ARgos and ALtiKa (SARAL), were used to measure sea surface heights (SSH). Altimetry-derived SSH was validated for the southern Bay of Biscay, using records from seven tide gauges located along the French Atlantic coast. More detailed comparisons were performed at La Rochelle, as this was the only tide gauge whose records covered the entire observation period for the different radar altimetry missions. The results of the comparison between the altimetry-based and in-situ SSH, recorded from zero to five kilometers away from the coast, had root mean square errors (RMSE) ranging from 0.08 m to 0.21 m, 0.17 m to 0.34 m, 0.1 m to 0.29 m, 0.18 m to 0.9 m, and 0.22 m to 0.89 m for SARAL, Jason-2, Jason-1, ENVISAT, and ERS-2, respectively. Comparing the missions on the same orbit, ENVISAT had better results than ERS-2, which can be accounted for by the improvements in the sensor mode of operation, whereas the better results obtained using SARAL are related to the first-time use of the Ka-band for an altimetry sensor. For Jason-1 and Jason-2, improvements were found in the ocean retracking algorithm (MLE-4 against MLE-3), and also in the bi-frequency ionosphere and radiometer wet troposphere corrections. Close to the shore, the use of model-based ionosphere (GIM) and wet troposphere (ECMWF) corrections, as applied to land surfaces, reduced the error on the SSH estimates.

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“…Nadir altimeters emit a radar pulse in the nadir direction (or local vertical, Figure 1) and then record the radar echo using a pulse compression technique. This record, also known as the waveform, contains the value of the returned power as a function of time or, equivalently, of distance between the radar and the reflectors (Chelton et al, 2001;Frappart et al, 2017). The two-way travel time (T), given by the leading edge of the waveform signal, is estimated accurately using a "retracking" algorithm applied to the waveforms by the mission processing centre.…”

Section: Introductionmentioning

confidence: 99%

“…However, estimates of the range R need to be corrected for propagation delays of the radar signal within the atmosphere (these corrections are labelled ΔR propagation ) and for some known geophysical signals that affect measurement (these corrections are labelled ΔR geophysical ) (e.g. Chelton et al, 2001;Frappart et al, 2017). In our study, ΔR propagation includes the ionosphere correction, the dry troposphere correction, and the wet troposphere correction (for more details, see Biancamaria et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Validation of Jason-3 tracking modes over French rivers

Biancamaria

Schaedele

Blumstein

et al. 2018

Remote Sensing of Environment

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Satellite nadir radar altimeters have been widely used to measure river and lake surface water elevations. They can now retrieve the elevations of some rivers less than 200 m wide. However, as these satellite missions are primarily designed to observe ocean surface topography, they are not always able to observe continental surfaces. For steep-sided rivers (i.e. in river valleys no more than a few km wide and surrounded by slopes over 50 m high), altimeters tend to observe the top of the surrounding topography rather than the river itself. The Jason-3 altimetry mission, launched in January 2016, has an alternative instrument operation mode, the so called Open-Loop (OL) or Digital Elevation Model (DEM) tracking mode. This mode is intended to help overcome this issue, by using an on-board DEM. However it was not used in 2016 as the operational mode because of difficulties in defining an accurate on-board global-scale DEM. Mainland France has been chosen to test the OL tracking mode, as water masks and DEMs of sufficient accuracy are available. Following the launch of Jason-3, Jason-2 (its predecessor) was maintained on the same nominal orbit as its follow-on, for more than 6 months. During this tandem period, data from the first 10 Jason-3 cycles (a Jason-2/-3 cycle corresponds to 10 days) were acquired in the traditional Closed-Loop (CL) tracking mode. Jason-3 data from the last 13 cycles were acquired in OL tracking mode. Jason-2 was always in CL tracking mode. Compared to nearby in situ gages and for river wider than 100 m, Jason-3 water elevation anomalies have a RMSE between 0.20 and 0.30 m for most reaches. Jason-3 performance over narrow rivers is similar to that of Jason-2. In CL tracking mode, Jason-3 altimeter tends to be locked over the surrounding topography more frequently than Jason-2 (due to the specific post-launch Jason-2 altimeter tuning). This study shows that Jason-2 observed 60% of river reaches studied (48 of 86 reaches), whereas Jason-3 in 3 OL tracking mode was able to measure all river reaches for every cycle. This result clearly highlights the significant advantages of the OL tracking mode for observation of steep-sided rivers. However, further investigations are required to compute an accurate on-board global-scale DEM and to determine those locations where the use of OL tracking mode is or is not appropriate.

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Satellite Altimetry: Principles and Applications in Earth Sciences

Cited by 15 publications

References 165 publications

Monitoring Sea Level and Topography of Coastal Lagoons Using Satellite Radar Altimetry: The Example of the Arcachon Bay in the Bay of Biscay

Monitoring Sea Level and Topography of Coastal Lagoons Using Satellite Radar Altimetry: The Example of the Arcachon Bay in the Bay of Biscay

Multi-Satellite Altimeter Validation along the French Atlantic Coast in the Southern Bay of Biscay from ERS-2 to SARAL

Validation of Jason-3 tracking modes over French rivers

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