Nicolas Roussel

Power tools for copying and moving: useful stuff for your desktop

Copy and move operations have long been supported by interactive desktops through various means. But the growing number of on-screen objects makes these means harder to use. In this note, we present new tools and techniques to enhance the existing ones: a selection, copy and drag history manager; two techniques to expose the users desk and leaf through stacks of overlapping windows; and a technique that integrates the previous two with conventional drag-and-drop.

Detection of Soil Moisture Variations Using GPS and GLONASS SNR Data for Elevation Angles Ranging From 2° to 70°

We propose a Global Navigation Satellite System-Reflectometry (GNSS-R) interference pattern technique method to estimate the temporal variations of the soil moisture content of the ground surrounding a single geodetic antenna. Three parameters can be inverted from GNSS signal-to-noise ratio (SNR) acquisitions: amplitude/phase of the multipath contribution to SNR and effective antenna height. Our method is applied to determine the surface moisture of a bare soil at Lamasquère, France, from February 5 to March 15, 2014. First, only data from low satellite elevation angles (<; 30°) are taken into consideration and are compared with independent 2-cm depth soil moisture records. The combination of the measurements from all GPS satellites, tested for the first time, improves the quality of the results with a correlation coefficient reaching 0.95, with a 10-min sampling rate. Our study shows that it is also possible to take high satellite elevation angles into account, even if the sign of the correlation appears to be reversed w.r.t. data from low satellite elevation angles. The cutoff angle where the sign of the correlation reverses seems to be around 30°. With regard to the effective antenna height, only a very low correlation is observed for high satellite elevation angles. We propose a new inversion method taking the pseudo-dynamic of the surface into account, which increases the correlation from 0.39 to 0.82. By normalizing and inverting the time series obtained from either low or high satellite elevation angles, it is possible to combine them, which enhances the results (correlation = 0.95).

Reflectometry With an Open-Source Software GNSS Receiver: Use Case With Carrier Phase Altimetry

An open-source GNSS software receiver allows to have full access to the signal processing and to make add-ons to the source code in order to obtain the desired GNSS reflectometry processing. The direct signal is processed in the standard way, its tracking loops replica are tapped to have a robust processing of the reflected signal in a master-slave configuration, with the very same carrier replica used to correlate the reflected signal. In addition, the data bit sign is wiped off, which allows to extend the coherent integration time (CIT) well beyond the usual 20-ms limit on the reflected way. This allows having a straightforward and accurate measurement of the Amplitude Ratio and Differential Carrier Phase between the direct and reflected signals. The possible applications are precise carrier phase altimetry and any application requiring signal amplitude ratio, or reflected signal Delay Map, with single or dual polarization, this include code altimetry, humidity, biomass, soil roughness, ocean surface wind and wave height, and snow and ice characteristics retrieval. This software is intended to be used as a research tool. It has been tested for carrier phase altimetry on real data sets collected in rather calm water conditions: at the 60-m Cordouan Lighthouse, and during a 600- m high ATR42 flight over a lake. In both cases, continuous carrier phase measurement with a centimeter level precision was obtained when extending the CIT up to 500 ms. Increasing the CIT beyond 20 ms is the key to improve carrier phase altimetry robustness.

The 2013 Ibiza Calibration Campaign of Jason-2 and SARAL Altimeters

This study presents the results of the 2013 Ibiza (Western Mediterranean) calibration campaign of Jason-2 and SARAL altimeters. It took place from 14 to 16 September 2013 and comprised two phases: the calibration of the GNSS (Global Navigation Satellite System) buoys to estimate the antenna height of each of them and the absolute calibration to estimate the altimeter bias (i.e., the difference of sea level measured by radar altimetry and GNSS). The first one was achieved in the Ibiza harbor at a close vicinity of the Ibiza tide gauge and the second one was performed at ∼ 40 km at the northwest of Ibiza Island at a crossover point of Jason-2 and SARAL nominal groundtracks. Five buoys were used to delineate the crossover region and their measurements interpolated at the exact location of each overflight. The overflights occurred two consecutive days: 15 and 16 September 2013 for Jason-2 and SARAL, respectively. The GNSS data were processed using precise point positioning technique. The biases found are of (−0.1 ± 0.9) and (−3.1 ± 1.5) cm for Jason-2 and SARAL, respectively.

Applications of GNSS-R in Continental Hydrology

Abstract: GNSS (Global Navigation Satellite System) Reflectometry (GNSS-R) is a bistatic radar remote sensing technology (transmitters and receivers are not in the same place) that uses microwave signals of opportunity from radio navigation such as the Global Positioning System (GPS). It extends and complements existing techniques for observation of the Earth by multiplying the number of transmitters (satellites in different positioning constellations) and receivers through the use of ground measurement networks, such as the permanent GNSS network in France (Reseau permanent GNSS, RGP) or the Plate Boundary Observatory (PBO) in the western United States, and allowing new measuring geometries.

User's issues in crossmedia applications

Technology allows users to interact with a wide variety of information and services. However, more and more users need to integrate complementary content to previously accessed information. Crossmedia applications combine different information pieces, which are stored in different media, as a continuous story. Our study selects the particular case of combining printed material and internet resources for the purpose of delivering complementary information to users. Our investigation conducts a workshop with users composed of a scenario-driven interview and a talk-aloud protocol. This experiment reveals the behavior and difficulties of users when they are combining digital and non-digital media to gather complementary information. In addition, some recommendation is suggested focused on the improvement of the users experience in crossmedia application that should be considered by designers.

The Reflected Global Navigation Satellite System (GNSS-R): from Theory to Practice

Abstract: If we consider all remote sensing systems, the system that has the largest constellation, which is the most used in the world, is undoubtedly the Global Navigation Satellite System (GNSS). This system has shown a high level of performance in geodesy, meteorology and many other areas of geophysics. However, this remote sensing tool has gained new momentum with the use of signals that are usually unwanted in conventional methods: reflected signals. This opportunistic method is an evolution of the GNSS and was named reflected GNSS or GNSS-R. There are numerous challenges for the GNSS-R because with the launch of new satellites (e.g. Galileo, BEIDOU/COMPASS), the quality and density of source signals is improving day by day, with an increasing number of satellites in orbit. It represents an undeniable complementarity with respect to other dedicated remote sensing systems, as it allows natural environmental phenomena to be monitored at a high temporal frequency. It also allows, as we shall see, the monitoring of many environmental problems: altimetric monitoring of ocean waters, coastal areas, inland waters, but it is also likely to provide other essential information such as soil moisture level, snow depth, and monitoring of flooded areas. That is surely one of the main advantages of this method, born by chance from the incongruous reflection of the GNSS electromagnetic wave on various surfaces (soil, water, snow, vegetation, target detection such as a boat, etc.).

Detection of soil moisture content changes by using a single geodetic antenna: The case of an agricultural plot

As multipaths still represent a major problem for reaching precise GNSS positioning, the mitigation of their influence has been widely investigated. However, previous studies have lately proposed to use these interferences of GNSS electromagnetic waves to estimate parameters related to the reflecting surface (e.g., antenna heights, rugosity,...). Variations of the nature of the surface is likely to modify the properties of the reflected waves, and consequently lead to variations of amplitude / phase of the signal-to-noise ratio (SNR), e.g. recorded at 1 Hz by a GNSS receiver. By analyzing the time variations of SNR measurements linked to the dielectric constant of the surrounding soil, we use a method to recover the local fluctuations of the soil moisture content. It is simply based on the obvious linear correlation between SNR amplitude / phase and retrieved antenna height time series and independent measurements of humidity probe at 2 and 5 cm depths. This method of combination is applied to determine soil moisture in a corn and soya field at Lamasquère, France, for 21 successive days. Results show a good correlation (e.g. 0.96 with GPS PRN-01 satellite) between SNR inversion and humidity probes for most satellites.

High rate GNSS measurements for detecting non-hydrostatic surface wave. Application to tidal borein the Garonne River

Abstract This study presents the results of the use of high frequency Global Navigation Satellites Systems (GNSS) data for the detection and the characterization of tidal bores. The experiment took place the 31st of August 2015 in the Garonne River, at 126 km upstream the mouth of the Gironde estuary. The GNSS data acquired on a buoy at a sampling rate of 20 Hz were processed with a differential GNSS technique using the RTKLIB freeware. GNSS-based elevation of the free surface provides accurate estimates of the tidal bore first wave amplitude (1.34 m) and period (3.0 s). These values were in good agreement with values obtained using ADCP measurements.

Modeling of GNSS multipath signals for altimetry applications using signal to noise ratio data

Multipaths are one of the major source of error for positioning applications using Global Navigation Satellite Systems (GNSS). During the last decade, several studies demonstrated the potential of the inversion of Signal to Noise Ratio (SNR) due to multipaths for estimating environmental parameters such as sea level, soil moisture, and snow depth variations, vegetation growth and biomass quantification. Here, we propose i) a modeling approach contribution of the multipath signals to the SNR, ii) an inversion technique of the receiver height based on the modeled SNR.