OBSERVATIONS – Surface and Boundary Layer conditions (LIAISE)

  Oral Presentations                    
No. Name Affiliation Co-authors Abstract L-WG1 L-WG2 L-WG3 OBS RS MOD
8 Bech, Joan Universitat de Barcelona –
Bech, Joan – University of Barcelona, Spain;
Udina, Mireia – University of Barcelona, Spain;
Peinó, Eric – University of Barcelona, Spain;
Polls, Francesc – University of Barcelona, Spain;
García-Benadí, Albert – University of Barcelona, Universitat Politècnica de Catalunya, Spain;
Balagué, Marta – University of Barcelona, Spain;
Paci, Alexandre – CNRM-SNRS, Meteo-France, France;
Boudevillain, Brice – CNRS, IRD, Université Grenoble Alpes, France;
An overview of precipitation observations and related microphysical processes during the LIAISE-2021 field campaign

Within the framework of the LIAISE-2021 field campaign, the WISE-PreP project was carried out to study precipitation processes aiming to characterize possible differences in precipitation induced by surface characteristics (irrigated vs non-irrigated areas). Instrumentation deployed during the 2021 campaign included three sites equipped each with a vertical radar Doppler MRR (Micro Rain Radar) and a PARSIVEL laser disdrometer, plus an additional PARSIVEL disdrometer, covering both irrigated and non-irrigated sites. Time series of vertical precipitation profiles and in-situ drop size distributions were recorded to study microphysical processes and related variables including precipitation intensity or convective vs stratiform rainfall regimes. Results show higher accumulated precipitation in the non-irrigated area (eastern area) than those in irrigated area (western area) in summer 2021, a feature also observed in summers for a previous reference period (2010-2019). Maximum and minimum daily temperatures were higher in irrigated areas than in non-irrigated areas. Both results are consistent with current climatology based on monthly precipitation and temperature that indicate the existence of a zonal gradient that increases semi-arid conditions (drier and warmer) from the east to the west. Disdrometer derived 1-min rainfall rate distributions presented some differences between the irrigated and non-irrigated areas during summer, unlike the other seasons when surface conditions are more similar in both areas. This research was supported by projects WISE-PreP (RTI2018-098693-B-C32) and ARTEMIS (PID2021-124253OB-I00) and the Water Research Institute (IdRA) of the University of Barcelona.
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6 Canut, Guylaine CNRM Météo-France, CNRS –
Lothon, M. – LAERO, Univ. of Toulouse, CNRS, UPS, France;
Joly, L. – GSMA, Université de REIMS, CNRS, France;
Boone, A. – CNRM-Météo-France, France;
Couzinier, J. – CNRM-Météo-France, France;
Etienne, J.C. – CNRM-Météo-France, France;
Moulin, E. – CNRM-Météo-France, France;
Roy, A. – CNRM-Météo-France, France;
What turbulent processes in the lower atmosphere are observed over a irrigated surface during the LIAISE campaign?

During the LIAISE campaign an intensive 15-day period was dedicated to documenting the atmospheric boundary layer over 2 high contrasted areas : one irrigated intensively cultivated area, and one non-irrigated semi-arid area. Numerous similar measurements were made at the 2 super sites in July 2021. At La Cendrosa, the super site in the irrigated area, the turbulent processes between the surface and the atmosphere were well documented by an instrumented 50m mast, a turbulent probe on-board a tethered balloon, the french SAFIRE ATR 42 research aircraft, hourly radiosondes and wind profilers. The complementarity of these observations allows us to understand the vertical structure of the atmospheric boundary layer during this period of high water demand by the vegetation. In this study, a first part will be dedicated to the validation of a new equipment of fast humidity measurement under tetheredballoon allowing the estimation with the eddycovariance method of turbulent fluxes. Then the study will be based on the complementarity of its observations which allow to highlight the presence of limited vertical boundary layer and weak turbulence. Indeed, the measurement of sensible and latent heat fluxes on the 50m mast and under the tetheredballoon allow to identify a very fast decrease with the altitude of the turbulence. Also, the radiosondes and wind profilers highlight the establishment of thermal breezes and complex boundary layers on certain days. This strong heterogeneity is well documented by LIAISE field campaign, which will allow us to improve our knowledge on the impact of the strong contrats on the local circulation. This study takes a review of the available observations to address process issues. This work will be followed by a complementary study of the two contrasting sites in order to identify the different processes and the local circulation taking place between the two areas.
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3 Jimenez, Maria A. Universitat de les Illes Balears –
Grau A. – Universitat de les Illes Balears, Spain;
Martínez-Villagrasa D. – Universitat de les Illes Balears, Spain;
Cuxart, J – Universitat de les Illes Balears, Spain;
Characterisation of the marine-air intrusion Marinada in the eastern Ebro subbasin

The eastern Ebro basin is composed of an extensive irrigated plain, surrounded by rainfed slopes and wooden mountain ranges and open to the west to the agricultural western Ebro basin. The sea breeze generated at the coast is able to surmount the Catalan prelitoral range through its lowest heights, reaching the basin in the afternoon by its easternmost part. It is a well-known feature in the region, called Marinada.
A network of Automatic Weather Stations is used here to analyze a period of 19 years (2003-21). A filtering procedure is developed which selects the events when the Marinada is present, based on detecting clear sky, weak wind conditions and the wind direction from the coast in the afternoon.
The analysis of these days show that the Marinada propagates along the basin, while observations of the specific humidity show a sudden increase as the temperature cools down, indicating a cold and humid advection. It is also found that the timing of the arrival of the Marinada depends on the mesoscale/synoptical circulations already present in the region (westerlies or a thermal low). As a example, the Marinada events reported during the intensive period of the LIAISE are further analyzed.
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10 Kim,Ed NASA-GSFC –
Wu, Albert – NASA, USA;
Izadkhah, Hessam – NASA, USA;
Abraham, Saji – NASA, USA;
FINE-resolution slap soil moisture observations during LIAISE

A summer 2021 European airborne field campaign—the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) campaign—presented an opportunity to explore passive soil moisture sensing with footprints as small as 100x200m, contributing a key measurement to LIAISE and providing a rare opportunity to gain detailed insight into the water/energy/carbon exchanges at such plot-scale resolution over a 17 x 5 km area.
NASA Goddard’s Scanning L-band Active Passive (SLAP) sensor—an airborne simulator of the Soil Moisture Active Passive (SMAP) satellite—made nine soil moisture flights near Lleida, Spain during 15—29 July, 2021. We present soil moisture imagery and histograms spanning irrigated and non-irrigated land and their response to a precipitation event followed by a drydown.
A total of nine science flights were made during 15—29 July.  The majority of the flights were at an altitude of 300m (1000ft) above ground level (AGL), where the radiometer half-power footprint size is slightly less than 100 x 200m.  Two flights were at the radar minimum operating altitude of about 800m (2500ft) AGL, where its footprint size is approximately 220 x 470m, and the radiometer footprints are 10% smaller.  A key feature of SLAP is its thin packaging—only 23 cm high—enabling operation on relatively small aircraft.  Since 2013, SLAP has been flying on NASA Langley’s B200 and UC-12 King Airs.  One flight each was made on the mornings of July  15, 16, 17, 25, 27, 28, and 29. On July 24, a second afternoon flight was added to explore the diurnal signal. 
At the 100 x 200m resolution, a 5 x 17 km area (the “GLORI box”) was observed.  When collecting active/passive observations, a larger 20 x 20 km area was observed.   Radio frequency interference (RFI) was occasionally observed in the vicinity of the small towns throughout these areas. 
The soil moisture algorithm includes similar physics to the algorithm used by SMAP and uses a number of ancillary data parameters such as soil temperature, texture, vegetation opacity, etc.
Example images of soil moisture over the GLORI box will be presented—first using uniform ancillary parameter values in the soil moisture algorithm, and then using the recent detailed ancillary data.  The wide-scale dry conditions before the precipitation of July 26 are easily visible.  The wetting and following drydown following July 26 are also easily visible, as well as the difference between irrigated and non-irrigated areas.    These examples will help users better understand the SLAP data, and how to use it.
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7 Lothon, Marie Laboratoire d’Aérologie, CNRS, Université de Toulouse –
Canut, G. – CNRM-Météo-France, CNRS, France;
Avrillaud, S. – CNRM-Météo-France, CNRS, France;
Lohou, F. – LAERO, Univ. Toulouse, CNRS, France;
Philibert, A. – IRAP, LAERO, Un Toulouse, CNRS, France;
Bezombes, Y. – LAERO, Univ. Toulouse, CNRS, France;
Etienne, J-C – CNRM-Météo-France, CNRS, France;
Vial, A. – LAERO, Univ. Toulouse, CNRS, France;
Amestoy, J. – CEA, DAM, DIF, France;
André, G. – CNRM-Météo-France, CNRS, France;
Bellec, H. – SAFIRE, Météo-France, CNRS, CNES, France;
Boone, A. – CNRM-Météo-France, CNRS, France;
Brilouet, P.-E. – SAFIRE, Météo-France, CNRS, CNES, France;
Canonic, J.-C. – SAFIRE, Météo-France, CNRS, CNES, France;
Cluzeau, M. – SAFIRE, Météo-France, CNRS, CNES, France;
Desbios, J.-P. – SAFIRE, Météo-France, CNRS, CNES, France;
Duchanoy, D. – SAFIRE, Météo-France, CNRS, CNES, France;
Ehses, G. – SAFIRE, Météo-France, CNRS, CNES, France;
François, E. – CNRM-Météo-France, CNRS, France;
Garrouste, O. – CNRM-Météo-France, CNRS, France;
Hüe, A. – SAFIRE, Météo-France, CNRS, CNES, France;
Jiang, T. – SAFIRE, Météo-France, CNRS, CNES, France;
Lainard, C. – SAFIRE, Météo-France, CNRS, CNES, France;
Lernould, J. – SAFIRE, Météo-France, CNRS, CNES, France;
Meslin, P.-Y. – IRAP, Un Toulouse, France;
Pagan, G. – CNRM-Météo-France, CNRS, France;
Pique, E. – LAERO, Univ. Toulouse, CNRS, France;
Seurat, G. – SAFIRE, Météo-France, CNRS, CNES, France;
Starck, F. – LAERO, Univ. Toulouse, CNRS, France;
Unger, V. – CNRM-Météo-France, CNRS, France;
Vergez, G. – SAFIRE, Météo-France, CNRS, CNES, France;
Variability of boundary layer vertical structure over the strong surface discontinuity of LIAISE

During the LIAISE campaign an intensive 15-day period was dedicated to documenting the atmospheric boundary layer over 2 high contrasted areas : one irrigated intensively cultivated area, and one non-irrigated semi-arid area.  Two supersites were highly instrumented in a similar way over the 2 respective surfaces. Among other instruments, 2 UHF wind profilers were deployed, which allow to document the vertical structure of the boundary layer dynamics (wind, shear and turbulence) and the evolution of the convective boundary layer depth. Complementarily to this, the French SAFIRE ATR42 aircraft made 8 flights, with in situ fast measurements of wind, temperature, and moisture.
In a first part, we will present the corresponding data process and the available dataset that was composed, based on the measurements of the UHF wind profilers and the ATR 42 aircraft, including added value parameters processed from the primary geophysical variables.
In a second part, we will present a first analysis of the two datasets, which on some days and variables reveal a very marked contrast of the low troposphere from one site to the other, and potential circulations. We will attempt to connect the differences among cases with the regional circulation.
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2 Mol, Wouter Wagenigen University –
Netherlands, The
Heusinkveld, Bert – Wageningen University, the Netherlands;
Hartogensis, Oscar – Wageningen University, the Netherlands;
Van Heerwaarden, Chiel – Wageningen University, the Netherlands; 
High resolution spatiotemporal variability of solar irradiance and water vapour at La Cendrosa

Solar irradiance is the external driving force of evapotranspiration, and varies across a wide range of spatiotemporal scales down to seconds or meters, mostly due to clouds. On top of that, vegetation adds extra fluctuations at scales below one tenth of a second, making in-canopy solar irradiance highly variable. The solar radiation that penetrates vegetation also shifts in wavelength distribution and in partitioning of direct and diffuse. As radiation is fundamental in the process of evapotranspiration, we have deployed a network of radiometers at La Cendrosa during LIAISE to measure above-canopy solar irradiance variability. An additional radiometer was placed inside the growing alfalfa to measure in-canopy variability as well. These radiometers are custom designed to capture spatial, temporal, and spectral variations in incoming solar radiation. Each radiometer samples 18 wavelengths at 10 Hz.
I will present a few cloud-driven patterns as observed from this network to illustrate the primary source of heterogeneity in solar radiation, and two results of the measurements in the context of evapotranspiration (ET). The weather during our measurement period, July 2021, was often clear-sky, which allowed us focus on variations in the spectra or in-canopy variability in the absence of the complexity that clouds introduce. Firstly, using the water vapour absorption bands in our measured spectra, we derive vertically integrated water vapour. Intra-day variability and trends are distinctly different from what ERA5 provides, and indirectly include information on local to regional scale variability of ET. Secondly, the radiometer that was placed on the soil amidst the growing alfalfa shows a shift from stable to highly variable (sub-second) irradiance within the two week measurement period. These observations are useful for checking model assumptions, setting boundary their conditions, and understanding the complex behaviour of solar irradiance under a range of different conditions.
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9 Ouaadi, Nadia Centre d’Etudes Spatiales de la Biosphère (CESBIO), CNRS –
  Intercomparison of high spatial resolution surface soil moisture products derived from microwave data

High spatial resolution surface soil moisture (SSM) products are becoming increasingly available nowadays either derived from passive microwave data via SMAP and SMOS disaggregation algorithms, or from high resolution radar data in particular using free products from Sentinel-1 sensor. In the literature, there are numerous intercomparison studies of soil moisture products at coarse resolution but there is a lack of such studies at high spatial resolution that are more relevant for plot-scale applications. In this context, this work is devoted to an intercomparison study of high spatial resolution SSM products over the Urgell region of Catalonia, Spain within the frame of LAISE project and of the associated ground campaign carried out in summer 2021. Simultaneously, a large database of in situ SSM measurements was collected at two different sites in this region in 2021. The first site (referred to as Site I) consists of 11 fields of different annual crops where SSM was automatically collected at a one-hour time step during the growing season in winter or summer. The SSM database for the second site (referred to as Site II) is collected manually using thetaprobes during several field campaigns conducted on 22 fields over two weeks in July. For the satellite SSM products, 4 products are initially used in this study: i) Product at the plot scale derived from a synergy of Sentinel-1 and Sentinel-2 using a machine learning algorithm, made available via the Theia website (hereinafter referred to as Theia product); ii) Product at 14 m resolution derived from the Sentinel-1 backscattering coefficient and the interferometric coherence using a brute-force algorithm (ρ product); iii) Product at 20 m resolution disaggregated from SMAP using Sentinel-3 and Sentinel-2 data (SMAP20m product); and iv) Product at 100 m resolution derived from SMAP disaggregated using Landsat 7 and 8 (SMAP100m). The latter product gave similar results as SMAP20m on summer fields, but was discarded as its availability is limited due to the low temporal resolution of Landsat combined with the cloud cover, especially in winter when the product is almost unavailable. Comparing the other three products to the entire in situ database at both sites, the correlation is 0.47, 0.34, and 0.22 using the ρ, Theia, and SMAP20m products, respectively. Similarly, the bias is 0, -0.04 and -0.08 m3/m3 while the RMSE is quite similar between products with 0.10, 0.11 and 0.12 m3/m3 for the three products in the same order. The lower accuracy of Theia and SMAP20m compared to ρ could partially be related to a saturation effect of the two products. Indeed, over Site II where the SSM range was limited to 0.3 m3/m3, the correlation is =0.55 and 0.30 for Theia and SMAP20m, respectively. In contrast on Site I, the Theia and SMAP20m products are much less accurate as they saturate at about 0.3 m3/m3 while in situ SSM values reach =0.5 m3/m3. SMAP20m is otherwise poorer than the other two products even over Site II and this may be related to the use of Sentinel-2 optical data for disaggregation which do not contain SSM related information. The approach can however be improved by using thermal data in the perspective of new missions such as TRISHNA and LSTM with both high temporal and spatial resolution data.
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1 Siegmann, Bastian Forschungszentrum Jülich –
Quiros-Vargas, Juan – Forschungszentrum Jülich, Germany;
Krämer, Julie – Forschungszentrum Jülich, Germany;
Bendig, Juliane – Forschungszentrum Jülich, Germany;
Salattna, Saja – Forschungszentrum Jülich, Germany;
Rascher, Uwe – Forschungszentrum Jülich, Germany;
Measuring solar-induced chlorophyll fluorescence (SIF) across scales as a proxy of photosynthetic activity – First results from the LIAISE field campaign in July 2021

Remote sensing of solar-induced chlorophyll fluorescence (SIF) measured with remote sensing sensors is a key parameter to better understand plant functioning at different spatial and temporal scales. Due to the direct relationship between SIF and photosynthetic activity, SIF is important for the monitoring of gross primary productivity (GPP) and the early detection of vegetation stress before it becomes measureable with conventional, reflectance-based remote sensing proxies (e.g., vegetation indices).
The SIF signal is immediately released from chloroplasts after the absorption of sunlight and emitted as a continuous spectrum in the range of red and far-red light (650–850 nm). Since SIF is only a small part of reflected radiance (1-5%), its detection is challenging and requires precisely calibrated spectrometers providing spectral high-resolution data and a high signal-to-noise-ratio. In previous years, several studies have demonstrated the potential of proximal, unmanned aerial vehicle (UAV), airborne, and satellite sensors measuring SIF at different spatial scales and temporal resolutions.
In this presentation, we want to give an overview about the different SIF sensors and measurement techniques used during the intensive LIAISE field campaign in July 2021. Furthermore, we want to present first results of the measurements of the alfalfa field at La Cendrosa recorded at the different spatial scales starting from the leaf, continue with canopy close-range and unmanned aerial vehicle (UAV) up to the airborne scale.
As an outlook, we will address different SIF-related research topics, we are currently interested in, such as the scaling of SIF, and the SIF-GPP and SIF-soil moisture relationship. The large amount of soil, canopy and atmospheric data recorded during the intense field campaign in 2021 will facilitate further exploration of the potential and benefit of remotely-sensed SIF in characterizing the photosynthetic performance of plants.
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4 Vis, Gijs Technical University Delft –
Netherlands, The
Hartogensis, Oscar – Wageningen University, the Netherlands;
ten Veldhuis, Marie-Claire – TU Delft, the Netherlands;
Coenders, Miriam – TU Delft, the Netherlands;
Spatial temperature measurements using DTS in the LIAISE field campaign

In this study we introduce four Distributed Temperature Sensing (DTS) setups deployed at an irrigated alfalfa field site (La Cendrosa) as part of the LIAISE field campaign during 15-30 July 2021 in the north-east of Spain.  The DTS technique relies on the temperature dependence of Raman backscattering of light in a fibre optic cable. DTS provides spatially distributed temperature data over time. The type of profile (horizontal vs vertical), spatial- and temporal resolution and distance covered depend on the measurement configuration. We installed four DTS setups at La Cendrosa to explore field scale heterogeneity and potentially the presence of an internal boundary layer induced by the strong thermal contrasts found in the LIAISE domain.
We deployed a 1.6 mm Kevlar-reinforced fibre covering a total distance of 600 m, which measured temperature at 5 s and 25.4 cm resolutions. In this continuous cable we included three DTS set-ups: 1) a surface layer profile between 1.6 – 40 m with a 25.4 cm vertical resolution, 2) a canopy profile averaged horizontally over 2.5 m with cables at 8 vertical levels between 0 – 1 m height inside of the rapidly-growing alfalfa and 3) a soil profile between -0.48 – 0 m with a vertical resolution of 1.25 cm; the enhanced spatial resolution was obtained by winding the cable onto a coil that was installed in the soil. An overview of first results is given, with an emphasis on factors limiting accuracy and on potential use in further research.
A fourth set-up was a so-called “turbulence harp”, which used a thinner, faster optical cable (=0.5 mm) over a horizontal path of 70 m, measuring at four heights between 0.40 m and 2.05 m height. Measurements were made at 1 Hz and 12.7 cm resolution. However, the  smallest frequency resolved in the temperature spectrum turned out to be 0.15 Hz, likely because of the long response time of the cable. Despite the relatively course resolved scales of 0.15 Hz we were able to express turbulence intensity in terms of the structure parameter of temperature (C_T^2). We estimated C_T^2 both from the temperature time series along the DTS cables, as well as, and this is a novel approach, from the spatial temperature series over the DTS cable. The spatially determined structure parameter correlated with a sonic anemometer C_T^2 estimate, with a correlation coefficient of 0.88.
This work outlines the potential for using DTS in land-atmosphere interaction campaigns and provides a first step towards using DTS in capturing turbulent information along a spatial temperature series.
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5 Wrenger, Burkhard University of Applied Sciences and Arts Ostwestfalen-Lippe –
Wrenger, Hanno – University of Ostwestfalen-Lippe, Germany;
Martínez-Villagrasa, Daniel – Un of the Balearic Islands, Spain;
Miró, Josep-Ramon – Servei Meteorològic de Catalunya, Spain;
Price, Jeremy – Met Office, UK;
Cuxart, Joan – University of the Balearic Islands, Spain
Temperature and Wind Profiles Taken by an UAV during the LIAISE Campaign

Unmanned Aerial Vehicles (UAVs) have been operated as part of the LIAISE campaign in order to complement the ground based instruments, radiosondes and manned aerials. We used multicopters for imaging activities and meteorological profiles. For details about the multicopters, the imaging technology and the results see a separate poster  [1].
The Q17 multicopter used by our group during the LIAISE campaign for the vertical profiles is essentially instrumented with a Trisonica mini weather station providing wind speed, wind direction, T and RH. The vertical profiles were intended to monitor the establishment of the surface thermal inversion at the IRTA site in the evening and its destruction after sunrise. These measurements from surface to 120 m above ground level (agl) complement the information provided by the measuring devices in the surface layer and the WindRASS profile, which operates from 40 m agl upwards.
Furthermore an intercomparison is made between the eddy-covariance (EC) fluxes at 25 m above ground level provided by the UKMO tower at Els Plans and the estimates obtained from the 3D-Trisonica mounted on the Q17 multicopter during a late afternoon sea breeze event ("Marinada").
We show preliminary results for profiles of T and wind, and estimates of the corresponding turbulent fluxes and discuss the results of the intercomparison.

(1) B. Wrenger, H. Wrenger and J. Cuxart: UAV Based Imaging Activities during the LAISE Campaign. Abstract submitted to the 1ST LIAISE CONFERENCE AND DET CROSSCUT WORKSHOP.
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11 Zribi, Mehrez Centre d’Etudes Spatiales de la Biosphère (CESBIO) –
Dassas, Karin – CESBIO, France;
DeHaye, Vincent – CESBIO, France;
Fanise, Pascal – CESBIO, France;
Le Page, Michel – CESBIO, France;
Boone, Aaron – CNRM, France;
Analysis of GLORI airborne GNSS-R data for Soil Moisture estimation

Surface soil moisture is a key parameter in understanding the function of the soil–vegetation–atmosphere interface. It is also an essential parameter in the management of water resources related to irrigation [1]. Over the past thirty years, microwave remote sensing has shown great potential for estimating and monitoring this parameter. In this same context, GNSS-R measurements have also shown great potential for characterizing earth surface states and, particularly, surface soil moisture [2]-[3]. These measurements started first with in situ or airborne campaigns, illustrating good precision in the estimation of soil moisture and vegetation cover biomass at the same level as other active or passive microwave techniques [4].
The objective of this study is to propose a mapping of surface soil moisture (SSM) using airborne measurements based on the GLObal Navigation Satellite System Reflectometry Instrument (GLORI), a polarimetric instrument [5].
GNSS-R measurements were acquired at the agricultural Urgell site in Spain in July 2021. The GLORI instrument is derived from the conventional GNSS-R (cGNSS-R) family. It is a low-cost, 4-channel, highly versatile GNSS-R receiver built using mainly commercial off-the-shelf components. Measurements of direct and reflected GNSS signals are realized by two hemispherical GPS L1-L2 dual-polarization passive antennas, named the zenith antenna, which is mounted on the upper part of the aircraft fuselage, and the nadir antenna, which is mounted on the lower fuselage of the aircraft. The polarimetric instrument allows simultaneous acquisition of left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) and a complete analysis of the polarization effect on land surface characterization. Measurements are realized with the French research aircraft ATR-42. In parallel with the GLORI GNSS-R airborne acquisitions, various in situ measurements were made on these sites (roughness, soil moisture, and leaf area index) to validate the GLORI data and optimize the inversion algorithms. Intensive, collocated ground-truth measurements were recorded at the same time that the flights were made over the twenty-four reference fields (8 maize, 4 bare soils, 6 alfalfa, and 4 apple trees). The in situ measurements made at the reference fields were designed to determine the soil moisture, roughness, and vegetation characteristics.
An analysis of observable copolarization (right-right) reflectivity   and the cross-polarization (right-left) reflectivity  behaviors as a function of incidence angle is proposed. The angular effect is demonstrated to be very weak for the case of  . Linear modeling of this effect seems sufficient, with an effect linked to the development of vegetation cover. Thus, the slope of this relationship is between -0.014 dB/° and -0.048 dB/° for data ranging from an NDVI close to 0.2 to an NDVI close to 0.8. Regarding reflectivity in RR polarization, the angular effect is much greater, particularly for low incidence angles. A cosine function with two calibrated empirical parameters seems suitable to describe this relationship. For the polarization RL, the angular effect increases with the development of vegetation cover. Normalization of the reflectivity is thus proposed as a function of the incidence angle.
The sensitivity of reflectivities is then proposed as a function of surface soil moisture.  As demonstrated by other studies, reflectivity illustrates high sensitivity to SSM. For RL polarization, the sensitivity decreases from 29.61 dB/(m3/m3) for the class with NDVI<0.4 to 9.86 dB/(m3/m3) for the densest class (NDVI>0.4). An empirical model with two variables, soil moisture and the normalized difference vegetation index (NDVI), based on the principle of the tau-omega model is then considered for the inversion of GNSS-R reflectivity  and estimation of soil moisture. After calibration of the three parameters describing the model with a 3-fold cross validation approach, the validation allowed good precision for  , with an RMSE close to 0.07 m3/m3. A mapping of SSM is proposed from the  map at 100 m spatial resolution. The inversion model is thus used for each mesh considering the  information and the NDVI calculated from the Sentinel-2 data. Three maps are proposed for the three proposed flights acquired on three dates, 22/07/2021, 27/07/2021 and 28/07/2021. In all three cases, we first observe a clear contrast between the irrigated and rainfed zones, with higher moisture levels for the first one. This is obviously consistent with our field measurements and water resource use. In the nonirrigated part, we observe a certain homogeneity of the estimates due to the limitation of only rainfall effects and fewer variations in vegetation density.
In the context of the future launch of the European Space Agency's HYDROGNSS mission, these measurements should be enriched by other acquisitions covering new configurations, particularly with the L5/E5 configurations, to analyze their contribution to the monitoring of land surface states.
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  Poster Presentations                    
No. Name Affiliation Co-authors Abstract L-WG1 L-WG2 L-WG3 OBS RS MOD
P2 Belaid, Mohamed Ibrahim Institut de Recerca i Tecnologia Agroalimentàries (IRTA) –
Casadesus, Jaume – IRTA, Spain;
Cristobal, Jordi – IRTA, Spain;
Effect of hailnets above orchard canopies on the spectral signature of vegetation

Hail nets are used in orchards to protect vegetation from hail storms. Despite their protective role, these nets could have other effects. Few studies reported their influence on the microclimate, irrigation, tree growth, yield and fruit quality. This study aims to investigate their influence on the spectral signature of the vegetation as seen from above the nets. In fact, compared to reflectance obtained from remote sensing,  the reflectance below hail nets could be different. As a result, this could mislead the accurate estimation of vegetation indices and biophysical parameters of the orchard canopy.
In this first trial of the investigation, we assessed the reflectance above and below three types of hail nets  above apple canopies at the IRTA’s farm in Mollerussa. We used a fieldSpec Spectroradiometer to measure the reflectance spectra, at 3 different positions for each net type (left, center and right). We defined the transmittance of the net as the capacity of the net to transmit light to the canopy and we assumed that is the ratio of the incoming spectra below (Ib) net and the one above net (Ia), and that it is a function of the net. We checked that this ratio is constant for two types of nets. We studied the relationship between the Reflectance measured above and below (Ra, Rb). The results show an effect of the hail nets on the reflectance sampled from above, which can be modelled depending on the type of net and also to the circumstances of measurements.
This preliminary study confirms that  the presence of hailnets can incorporate a distortion on the reflectance as seen from above. More reliable approaches and more accurate estimates of the error incorporated by the nets are planned for the incoming season.
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P4 Capo, Julie CNRM – Météo-France, CNRS –
Capo, J. – CNRM-Météo-France, CNRS, France;
Roy, A. – CNRM-Météo-France, CNRS, France;
Canut-Rocafort, G. – CNRM-Météo-France, CNRS, France;
Brooke, J. – Met Office, United Kingdom;
Price, J. – Met Office, United Kingdom;
Boone, A. – CNRM-Météo-France, CNRS, France;
High frequency atmospheric soundings from the LIAISE field campaign

This poster will focus on radiosonde measurements made during the LIAISE field campaign from two sites: La Cendrosa and Els Plans. During the Special Observation Period (SOP) from 14th to 28th of July 2021, 272 radiosondes were released from two highly contrasting areas with different land cover. La Cendrosa site is situated within an irrigated zone on an Alfalfa crop while Els Plans site is located in a dry area with winter crops and seasonal bare soil. This hourly exploration from sunrise to sunset from radiosondes allows a very fine documentation in the growth of the convective boundary layer on two contrasting surfaces in terms of vegetation and soil moisture.
The sounding strategy during LIAISE SOP and the experimental equipment used will be described in detail at both sites. The post-processing applied on each parameter will also be explained in order to give anyone all of the information they need to work with the data. In particular, mixing ratio formulas will be discussed here.
The dataset (https://doi.org/1=+0.25326/322) described in this poster is of great importance to better understanding the processes between surfaces and the boundary layer and to finely evaluate atmospheric models. A comparison of boundary layer growth and vertical wind structure between the two sounding sites will be presented.

 * Boone, A., Best, M., Cuxart, J., Polcher, J., Quintana Seguí, P., Bellvert, J., Brooke, J., Canut-Rocafort, G., and Price, J.: Updates on the international Land Surface Interactions with the Atmosphere over the Iberian Semi-Arid Environment (LIAISE) Field Campaign- Gewex News, 31(4), 17-21., 2021.
* Dirksen, R. J., Bodeker, G. E., Thorne, P. W., Merlone, A., Reale, T., Wang, J., Hurst, D. F., Demoz, B. B., Gardiner, T. D., Ingleby, B., Sommer, M., von Rohden, C., and Leblanc, T.: Managing the transition from Vaisala RS92 to RS41 radiosondes within the Global Climate Observing System Reference Upper-Air Network (GRUAN): a progress report, Geoscientific Instrumentation, Methods and Data Systems, 9, 337–355.
* Jensen, M. P., Holdridge, D. J., Survo, P., Lehtinen, R., Baxter, S., Toto, T., and Johnson, K. L.: Comparison of Vaisala radiosondes RS41 and RS92 at the ARM Southern Great Plains site, ATM, 9, 3115–3129
* Kawai, Y., Katsumata, M., Oshima, K., Hori, M. E., and Inoue, J.: Comparison of Vaisala radiosondes RS41 and RS92 launched over the oceans from the Arctic to the tropics, Atmospheric Measurement Techniques, 10, 2485–2498
* Legain, D., Bousquet, O., Douffet, T., Tzanos, D., Moulin, E., Barrie, J., and Renard, J.-B.: High-frequency boundary layer profiling with reusable radiosondes, Atmospheric Measurement Techniques, 6, 2195–2205
* Rosoldi, M., Coppa, G., Merlone, A., Musacchio, C., and Madonna, F.: Intercomparison of Vaisala RS92 and RS41 Radiosonde Temperature Sensors under Controlled Laboratory Conditions, Atmosphere, 13
* Seity, Y., Brousseau, P., Malardel, S., Hello, G., Bénard, P., Bouttier, F., Lac, C., and Masson, V.: The AROME-France Convective-Scale Operational Model, Monthly Weather Review, 139, 976 – 991
* Vaisala: Met Office Intercomparison of Vaisala RS92 and RS41 Radiosondes, Tech. Rep., UKMO
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P1 Cuxart, Joan Universitat de les Illes Balears –
Martínez-Villagrasa, D. – University of the Balearic Islands, Spain;
Martí, B. – University of the Balearic Islands & CNRM, France;
Jiménez, M.A. – University of the Balearic Islands, Spain;
Price, J. – UK MetOffice, UK;
Best, M. – UK MetOffice, UK;
Brooke, J. – UK MetOffice, UK;
Thornton, J. – UK MetOffice, UK;
Miró, J.R. – Meteorological Service of Catalonia, Spain;
Groh, J. – University of Bonn & Forschungszentrum Jülich
Wrenger, B., Technical University Ostwestfalen-Lippe, Germany;
Conangla, L. – Polytechnical University of Catalonia, Spain;
Delanoe, J. – Université Paris-Saclay, France;
Cristobal, J. – IRTA, Spain;
Bellvert, J. – IRTA, Spain;
Girona, J. – IRTA, Spain;
Canut, G. – CNRM-MeteoFrance, France;
Special measurements in the LIAISE campaign area after the end of the 2021 Long Observation Period

The Long Observation Period (LOP) of LIAISE ended in early fall 2021. Then the instrumentation left after the July Special Observation Period (SOP, 15-29 July) was dismantled, including the French EC sites at La Cendrosa and Lake Ivars and the UHF profilers, the Dutch scillometers and the UIB EC station over corn. Nevertheless, instrumentation remained at IRTA-Mollerussa Experimental Field Station (IRTA-MEFS)in the  irrigated area and at Els Plans in the rainfed area with the aim to explore the surface-atmosphere interaction for a whole annual cycle.
At IRTA-MEFS the systems located in a wide clearing between fruit orchards and other irrigated crop fields are still running. A WindRASS system (SMC) provides profiles of virtual temperature and wind every 10 minutes with heights from 40 to 400 m above ground level. It is located next to a surface energy budget station (SMC) over well-watered short grass, together with two-levels of temperature and humidity (UIB) for the estimation of fluxes using the gradient approach. These devices provide reference values for the irrigated area in a continuous manner. Until November 2022, the UIB Surface Energy Budget (SEB) station, including a Krypton device (CNRM) and a numb, stayed over the IRTA lysimeter in the apple orchard to allow the exploration of ET during a full growing cycle of the apple trees in 2022, together with complementary instrumentation provided by IRTA.
At Els Plans site the remaining instrumentation was the UKMO 50-m,10-m and 2-m towers including EC systems and measurements in the Surface Layer and the upper soil, together with the FZJ smart-field-lysimeter and a complete SEB by UIB/OWL, resulting of the relocation of the instrumentation previously at the corn site at Mollerussa. With the aim of inspecting some specific fog events, a BASTA Radar (LATMOS) was deployed during winter. The main scientific goals threefold: i) to monitor the late spring drydown of the upper soil, which was difficult because during 2022 the area experienced the most severe drought since 2008; ii) to study the wintertime fog, which can be persistent in December and January and iii) to characterize the Stable Boundary Layer (SBL) regime, for which the early springtime was selected.
Two winter special observation periods (SOPs) took place, the first one in December/January during which a long persistent fog event took place (14-24 December), with radiosondes released every three hours between the 17th and 21st December. The second one, made between March 26th and April 8th 2022, was devoted to the SBL. It finally included five Intensive Observational Periods with frequent RS releases and multicopter vertical profilings. This SOP captured two devastating frost events in the beginning of April that led to the loss of a large part of the fruit production in the Lleida area.
Since the end of July 2022, after the dismantling of the UKMO material, at Els Plans remains the complete SEB station (UIB/OWL) and the smart-field-lysimeter (FZJ), allowing to contrast these measurements with those made at Mollerussa in the irrigated area. In the frame of the new Spanish-funded project WET-ARID involving international cooperation, these measurements will continue at least until summer 2025, with the aim to study the inter-annual variability at each site.
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P3 Wrenger, Burkhard University of Applied Sciences and Arts Ostwestfalen-Lippe –
Wrenger, Hanno – University of Ostwestfalen-Lippe, Germany;
Cuxart, Joan – University of the Balearic Islands, Spain;
UAV Based Imaging Activities during the LIAISE Campaign 2021

Unmanned Aerial Vehicles (UAVs) have been operated as part of the LIAISE campaign in order to complement the ground based instruments, radiosondes and manned aerials. We have been using two off-the-shelf UAVs (DJI M200 und DJI Mavic Pro multicopter) for imaging activities and a custom-built Q17 UAV dedicated to meteorological profiles. In this abstract we focus on our imaging activities which include thermal data acquisition complementing the profiles of T and wind and some service flights for other groups.
The DJI M200 was equipped either with a FLIR Duo Pro R thermal camera (640×512 pixels thermal and 12 MPixels VIS/RGB), with a MAPIR 3 multispectral camera (12 MPixels NGB) or with an X7 RGB camera (20 MPixels). The DJI Mapir Pro has a fixed RGB camera providing 12 MPixels. Both UAVs were operated in a heights between 20 and 60 m above ground level (agl) flying a grid path with an overlap of the images of 70-80 % in flight direction and lateral. The RGB and multispectral images are post-processed by AgiSoft Metashape or Pix4DFields software providing ortho images or digital elevation models (DEM) containing the photos of the whole flight. This process is based on Structure from Motion (SfM) algorithms which use tie points in multiple images in order to combine them.
The postprocessing pipeline for the thermal camera starts by applying non-uniformity corrections, the following processing pipeline is either similar to the RGB and multispectral pipeline or an individual analysis is applied.
The multicopter UAVs have flights times of 20-40 min depending on the payload. For long lasting imaging flights with flight  times larger than the one possible with a single battery package, the UAVs continue the flight after a replacement of the discharged batteries.
We show preliminary results for orthophotos and DEMs of the IRTA site, IRTA to Mollerussa, lake Ivars and the wineyard and examples of the thermal images for selected classes of the utilisation types in the vicinity of the IRTA site, e.g. orchard, orchard with shielding meshwork, corn field, irrigated grass or street.
The thermal images clearly show the temperature gradients, e.g. between orchard trees and the ambient soil or the corn field and the streets. This might support the analysis of local energy exchange processes in the multiple-meter to hectometer scale in the vicinity of the IRTA site and also the spatial analysis of evapotranspiration.
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