The light airborne reflectometer for GNSS-R observations (LARGO) instrument: Initial results from airborne and Rover field campaigns

Alonso-Arroyo, A.; Carmona, Á.; Monerris, A.; Rüdiger, Christoph; Walker, Jeffrey P.; Veliz, Giuseppe Francesco Forte; Pascual, Daniel; Park, Hyuk; Onrubia, R.

doi:10.1109/igarss.2014.6947376

Cited by 25 publications

(23 citation statements)

References 8 publications

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“…The LARGO instrument used in this field campaign is an improved version of a previous LARGO used before in [12], containing an additional switching matrix for calibration purposes. The LARGO instrument is a dual-channel instrument that estimates in real-time the coherent reflectivity ( …”

Section: Airborne Gnss-r Observations and Field Campaignmentioning

confidence: 99%

On the Synergy of Airborne GNSS-R and Landsat 8 for Soil Moisture Estimation

et al. 2015

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While the synergy between thermal, optical, and passive microwave observations is well known for the estimation of soil moisture and vegetation parameters, the use of remote sensing sources based on the Global Navigation Satellite Systems (GNSS) remains unexplored. During an airborne campaign performed in August 2014, over an agricultural area in the Duero basin (Spain), an innovative sensor developed by the Universitat Politè cnica de Catalunya-Barcelona Tech based on GNSS Reflectometry (GNSS-R) was tested for soil moisture estimation. The objective was to evaluate the combined use of GNSS-R observations with a time-collocated Landsat 8 image for soil moisture retrieval under semi-arid climate conditions. As a ground reference dataset, an intensive field campaign was carried out. The Light Airborne Reflectometer for GNSS-R Observations (LARGO) observations, together with optical, infrared, and thermal bands from Landsat 8, were linked through a semi-empirical model to field soil moisture. Different combinations of vegetation and water indices with LARGO subsets were tested and compared to the in situ measurements. Results showed that the joint use of GNSS-R reflectivity, water/vegetation indices and thermal maps from Landsat 8 not only allows capturing soil moisture spatial gradients under very dry soil conditions, but also holds great OPEN ACCESS Remote Sens. 2015, 7 9955 promise for accurate soil moisture estimation (correlation coefficients greater than 0.5 were obtained from comparison with in situ data).

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Section: Airborne Gnss-r Observations and Field Campaignmentioning

confidence: 99%

On the Synergy of Airborne GNSS-R and Landsat 8 for Soil Moisture Estimation

et al. 2015

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“…This is illustrated in Fig. 2 (blue dots, reflections over a water channel and colors changing over different fields) with GNSS-R data gathered from ~1 km height using the LARGO instrument [12]. Under coherent scattering conditions the spatial resolution is usually quantified as an ellipse given by the projection of the first (n = 1) Fresnel zone [10]:…”

Section: Introductionmentioning

confidence: 99%

Spatial Resolution in GNSS-R Under Coherent Scattering

Camps

2020

IEEE Geosci. Remote Sensing Lett.

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GNSS-R can be understood as a multi-static radar using satellite navigation signals as signals of opportunity. The scattered signals over sea ice, flooded areas-even under dense vegetation-, and in some cases over land show a significant coherent component. Under coherent scattering conditions, it is usually stated that the coherent signal component comes from an area equal to the first Fresnel zone. This work analyzes in more detail the spatial resolution in this forward scattering configuration, showing that, when coherent scattering is non-negligible, the spatial resolution is mostly determined by the geometry, and not by typical surface roughness values. As the scattering area around the specular reflection point increases and encompasses the first Fresnel zone, the received power increases and then it fluctuates as higher order Fresnel zones are included (rapid phase changes due to the spherical waves). These contributions may explain in part the large scattering encountered over inhomogeneous land regions, as these different contributions add or subtract, depending on the phase of the electric field, and are weighted by different scattering coefficients (i.e. changes in the dielectric constant and/or surface roughness, such in water ponds, or some agricultural fields…). Finally, over homogeneous targets, when all Fresnel zones are included, the received power tends asymptotically to the value obtained using the free-space propagation with a total path length equal to the sum of the path lengths, weighted by the reflection coefficient. This value can also be interpreted as coming from an effective region that is actually ~0.6 times the first Fresnel zone.

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“…The Light Airborne Reflectometer for GNSS-R Observations (LARGO) is a GNSS-R instrument designed and engineered by the Universitat Politècnica de Catalunya-BarcelonaTech for real-time measurements of the ground reflectivity, and from there inferring the soil moisture. This instrument has been tested in previous airborne experiments [7,8]. The objective of this work was not to directly retrieve soil moisture from the LARGO reflectivity, but to explore the relationships of the reflectivity map with a complete dataset of airborne thermal and optical data, together with field measurements as a ground truth data.…”

Section: Introductionmentioning

confidence: 99%

Airborne GNSS-R, thermal and optical data relationships for soil moisture retrievals

Sánchez

Alonso-Arroyo

González-Zamora

et al. 2015

2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)

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New remote sensing techniques based on the analysis of the Earth's surface-reflected signal from the Global Navigation Satellite Systems (GNSS-Reflectometry, or GNSS-R in short) are emerging. Soil moisture and vegetation status are some of the potential parameters that could be also retrieved from these sources. However, the complex interactions between the soil-vegetation interface can lead to spurious effects on the reflected signal. In order to study these effects, an airborne campaign was developed in an experimental area in Spain in August, 2014. A new GNSS-R-based instrument was flown together with thermal and optical cameras mounted on a paramotor. Ground measurements of soil moisture were taken during the flight. Maps at very high spatial resolution of reflectivity, Land Surface Temperature (LST) and the Digital Surface Model (DSM) were jointly analyzed, together with the ground observations. The results showed an important influence of the topography (i.e., the local incidence angle) on the GNSS-R reflectivity, and promising patterns relating reflectivity with soil moisture and LST were found. However, owing the dry soil and weather conditions during the experiment, further tests are needed over different environment and climatic conditionsPeer ReviewedPostprint (published version

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The light airborne reflectometer for GNSS-R observations (LARGO) instrument: Initial results from airborne and Rover field campaigns

Cited by 25 publications

References 8 publications

On the Synergy of Airborne GNSS-R and Landsat 8 for Soil Moisture Estimation

On the Synergy of Airborne GNSS-R and Landsat 8 for Soil Moisture Estimation

Spatial Resolution in GNSS-R Under Coherent Scattering

Airborne GNSS-R, thermal and optical data relationships for soil moisture retrievals

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