F. Soulat

GEROS-ISS: GNSS REflectometry, Radio Occultation, and Scatterometry Onboard the International Space Station

GEROS-ISS stands for GNSS REflectometry, radio occultation, and scatterometry onboard the International Space Station (ISS). It is a scientific experiment, successfully proposed to the European Space Agency in 2011. The experiment as the name indicates will be conducted on the ISS. The main focus of GEROS-ISS is the dedicated use of signals from the currently available Global Navigation Satellite Systems (GNSS) in L-band for remote sensing of the Earth with a focus to study climate change. Prime mission objectives are the determination of the altimetric sea surface height of the oceans and of the ocean surface mean square slope, which is related to sea roughness and wind speed. These geophysical parameters are derived using reflected GNSS signals (GNSS reflectometry, GNSS-R). Secondary mission goals include atmosphere/ionosphere sounding using refracted GNSS signals (radio occultation, GNSS-RO) and remote sensing of land surfaces using GNSS-R. The GEROS-ISS mission objectives and its design, the current status, and ongoing activities are reviewed and selected scientific and technical results of the GEROS-ISS preparation phase are described.

Tsunami Detection Using the PARIS Concept

On 26 December 2004 a tsunami generated by an earthquake with its epicentre in the Indian Ocean West of Indonesia caused a real human and material catastrophe in the region. After the event some proposals to establish a network of sensors for tsunami detection were put forward. This paper presents an alternative concept that can be applied from satellite, aircraft or from the coast, and which can complement such a network of sensors for fast tsunami detection. The concept makes use of GNSS signals reflected from the ocean’s surface to perform mesoscale ocean altimetry. The technique, designated PARIS (Passive Reflectometry and Interferometry System), aims at capturing fast topographic events happening on the ocean surface such as eddies and fronts. The paper includes details of some aircraft experiments whereby a PARIS altimeter was used to map a topographic signature with amplitude and wavelength similar to a tsunami in open ocean.

Oceanpal®: Monitoring sea state with a GNSS-R coastal instrument

Oceanpalreg is a coastal instrument developed at Starlab for operational remote sensing of the ocean surface, with potential direct applications to snow/ice mapping and soil moisture monitoring. The instrument is based on the exploitation of global navigation satellite systems (GNSS) and their augmentation systems (WAAS, EGNOS). The emitted signals provide an exceptional source of opportunity for passive remote sensing of the Earth. The use of GNSS reflections (GNSS-R) for sea-surface monitoring is a bistatic radar technique only requiring a receiving system. The concept has already been implemented for coastal platforms (few meters above the water), aircraft (1km to 10 km) and is being studied for space platforms (LEO, orbiting at 500-1000 km). The potential applications include sea-state, sea-surface altimetry and surface roughness, both for scientific and operational oceanography. We report on a recent long-term experimental and demonstration campaign, carried out at the Oceanpalreg Coeli station in the Barcelona Port during the period 2004-2007, with a real time web-based service. This campaign has been made possible through collaboration with the Barcelona Port Authority Environmental Monitoring Department (APB). The instrument was installed on a breakwater near the main entrance of the port, at 23 m over the sea-surface. We describe in this paper the successful long-term comparison between the data obtained by Oceanpal instrument and the observables recorded by two nearby buoys. Data used for this analysis cover a period of over one year, allowing a definitive evaluation of the performances of this GNSS-R based coastal instrument for SWH retrieval. We also review results from a weeklong phase altimetry campaign at the port of Vilagarcia.

Oceanpal: an instrument for remote sensing of the ocean and other water surfaces using GNSS reflections

Abstract This paper describes Oceanpal, an inexpensive, all-weather, passive instrument concept for remote sensing of the ocean and other water surfaces. Oceanpal is based on the use of reflected signals emitted from GNSS, and as such it is well grounded on the growing, long term GNSS infrastructure. As seen from the instrument, several GNSS emitters are simultaneously in view at any given time, providing separated multiple scattering points with different geometries. Reflected signals are affected by surface “roughness” and motion (i.e. sea state, orbital motion, and currents), mean surface height and dielectric properties (i.e. salinity and pollution). Oceanpal is envisaged to act as an accurate, “dry” tide gauge/surface monitoring system as a part of a future distributed ocean remote sensing network concept.

Innovative sea surface monitoring with GNSS-REflectometry aboard ISS: Overview and recent results from GEROS-ISS

GEROS-ISS (GEROS hereafter) stands for GNSS REflectometry, Radio Occultation and Scatterometry onboard the International Space Station. It is a scientific experiment, proposed to the European Space Agency (ESA) in 2011 for installation aboard the ISS. The main focus of GEROS is the dedicated use of signals from the currently available Global Navigation Satellite Systems (GNSS) for remote sensing of the System Earth with focus to Climate Change characterisation. The GEROS mission idea and the current status are briefly reviewed.

First results of GNSS-R coastal experiment in China

We report on the first time of GNSS-Reflection (GNSS-R) coastal experiment in Fujian province in the southeast of China. The experimental campaign began in September 2006 and the succeeding observation was kept until March 2007. Through the ocean reflected event recorded by the Oceanpal instruments, the direct and reflected correlation waveforms were obtained. We retrieved the Significant Wave Height (SWH) and Sea Surface Height (SSH) with these data. Then a method to compute the wave speed and direction by the delay of the autocorrelation waveforms was proposed. We present primary results here. With the continual measurements, we also studied the semidiurnal tides and paid our attention to the variations of amplitudes and phases of the tides. At last we present some problems occurred in this experiment and discussed the possible treatments to make the observing technique available in the seacoast of China.

Oceanpal/sup /spl reg// a GPS-reflection coastal instrument to monitor tide and sea-state

The Global Navigation Satellite Systems (GNSS, such as the GPS and GLONASS constellations) and their augmentation systems (WAAS, EGNOS) constitute premium sources of opportunity for passive remote sensing. By 2010, after the deployment of the European Galileo constellation, more than 50 GNSS satellites will be emitting self-calibrating, dual-frequency, rain-immune, L-band spread spectrum signals with long-term availability and stability. The use of GNSS reflections (GNSS-R) for sea-surface monitoring is a bistatic radar technique only requiring a receiving system. The concept was initially proposed by M. Martin-Neira in 1993 and has, since then, been successfully implemented in coastal receivers, in aircraft and recently, in space. The potential applications include sea-surface altimetry, sea-state, surface roughness, surface currents and salinity, both for scientific and operational oceanography. In this paper, we present Oceanpal/sup /spl reg//, a GNSS-R sensor developed by Starlab for operational coastal monitoring. It is an inexpensive, all-weather, dry and passive concept which can be deployed on multiple platforms, static (coasts, harbors, off-shore), and slowly moving (boats, floating platforms, buoys). In its present form, Oceanpal/sup /spl reg// can deliver two kinds of Level-2 products: the sea-surface height and the significant wave height.

GNSS Transpolar Earth Reflectometry exploriNg System (G-TERN): Mission Concept

The global navigation satellite system (GNSS) Transpolar Earth Reflectometry exploriNg system (G-TERN) was proposed in response to ESA’s Earth Explorer 9 revised call by a team of 33 multi-disciplinary scientists. The primary objective of the mission is to quantify at high spatio-temporal resolution crucial characteristics, processes and interactions between sea ice, and other Earth system components in order to advance the understanding and prediction of climate change and its impacts on the environment and society. The objective is articulated through three key questions. 1) In a rapidly changing Arctic regime and under the resilient Antarctic sea ice trend, how will highly dynamic forcings and couplings between the various components of the ocean, atmosphere, and cryosphere modify or influence the processes governing the characteristics of the sea ice cover (ice production, growth, deformation, and melt)? 2) What are the impacts of extreme events and feedback mechanisms on sea ice evolution? 3) What are the effects of the cryosphere behaviors, either rapidly changing or resiliently stable, on the global oceanic and atmospheric circulation and mid-latitude extreme events? To contribute answering these questions, G-TERN will measure key parameters of the sea ice, the oceans, and the atmosphere with frequent and dense coverage over polar areas, becoming a “dynamic mapper” of the ice conditions, the ice production, and the loss in multiple time and space scales, and surrounding environment. Over polar areas, the G-TERN will measure sea ice surface elevation (<10 cm precision), roughness, and polarimetry aspects at 30-km resolution and 3-days full coverage. G-TERN will implement the interferometric GNSS reflectometry concept, from a single satellite in near-polar orbit with capability for 12 simultaneous observations. Unlike currently orbiting GNSS reflectometry missions, the G-TERN uses the full GNSS available bandwidth to improve its ranging measurements. The lifetime would be 2025–2030 or optimally 2025–2035, covering key stages of the transition toward a nearly ice-free Arctic Ocean in summer. This paper describes the mission objectives, it reviews its measurement techniques, summarizes the suggested implementation, and finally, it estimates the expected performance.