Airborne campaign activities in the framework of the FLEX-ITA project

This contribution outlines the ongoing activities part of the project “FLEX Inland water and Terrestrial Airborne measurements and scientific exploitation” (FLEX-ITA), founded by the Italian Space Agency (ASI) and developed in collaboration between the University of Milano-Bicocca, CNR-IBE, CNR-IREA and FEM. The project aims to establish a network of experts in airborne and field campaigns to support the ESA FLEX mission. The two-year project includes a range of activities with the following key objectives: (i) deploy the airborne imaging spectrometer IBIS (Specim, Spectral Imaging Ltd., Finland) to acquire high-quality data for mapping the Solar-Induced Fluorescence (SIF); (ii) develop algorithms similar to FLEX mission processor for retrieving spectrally resolved SIF from airborne imagery; (iii) advance methods for Calibration/Validation (Cal/Val) of the FLEX mission through integrated airborne and ground-based measurements; (iv) promoting innovative approaches to SIF-based indicators for detection and monitoring of water stress in agriculture; and (v) exploiting FLEX-like measurements to improve phytoplankton characterization and evaluate in inland water environments. To achieve the project objectives, airborne campaigns are scheduled for the first and second years, supported by in-situ spectral, chemical/physical and physiological measurements. These efforts aim to build expertise in data acquisition, airborne sensor operation, processing methods, analysis, modelling and interpretation of the SIF data. Within this framework, the FLEX-ITA 2024 campaign was designed to acquire data through two distinct campaigns: (i) the “land” campaign focused on the early detection of water stress in agricultural crops, and (ii) the “water” campaign aimed at characterizing and quantifying aquatic phytoplankton in lakes. The campaigns involved simultaneous and coordinated data acquisitions using two high-resolution airborne imaging spectrometers, IBIS and HyPlant, which were co-installed on the same airborne platform (i.e., Cessna 208B Grand Caravan). This effort was made possible through a partnership between the FLEX-ITA project, CzechGlobe, and Forschungszentrum Jülich. The HyPlant airborne imaging spectrometer consists of the high-resolution FLUO module and the VIS-SWIR DUAL module. The FLUO operates in the red and near-infrared wavelengths (650–800 nm) with high spectral resolution (FWHM = 0.2 nm). The DUAL acquires imaging spectroscopy data across the 400–2500 nm range, providing key information for deriving biochemical and structural plant properties relevant to interpret SIF. The technical specifications of the IBIS sensor are similar to those of the FLUO module. Although the nominal characteristics of IBIS and FLUO are comparable, HyPlant is recognized as the first airborne sensor developed explicitly for SIF mapping. Since its introduction in 2012, it has been widely used in international campaigns related to the FLEX mission. In contrast, IBIS represents a newer commercial instrument with its full capabilities still being explored. The "land" campaign was conducted in Rispescia (Grosseto, Italy) from June 15 to July 7, 2024. Multiple flight lines were successfully acquired on June 22, 28, and 30, contributing to the diverse project objectives. These included multi-temporal flights on different days and times of the day, varying flight altitudes, and multi-angular observations. The irrigation manipulation experiment was conducted in the experimental area considering three agricultural crops (i.e., Sunflower, Sudan grass, and Lentils), each divided into well-irrigated and non-irrigated plots. During the experiment, field spectroscopy measurements were continuously collected using three FLOX spectrometers (JB-Hyperspectral, Germany) to measure SIF and canopy reflectance at various plots. Physiological measurements were also acquired throughout the campaign to characterize and monitor crop conditions. The "water" campaign covered the southwestern region of Lake Garda (Italy) where the CNR-IREA permanent station is located. On July 4th, airborne survey was conducted along seven flight lines, repeated at two different times of the day and at varying flight altitudes. Concurrently, an intensive field campaign was carried out with three distinct boats, encompassing a wide range of optical, biological, and physicochemical measurements, alongside water sampling at multiple depths across various sites. Laboratory analyses were performed to quantify chlorophyll-a, secondary pigments, coloured dissolved organic matter, and total suspended particles. Apparent optical properties, such as remote sensing reflectance, were measured using spectroradiometers including ROX, SR-3500, WISP-3, and HyperOCR, while phytoplankton fluorescence and backscattering were evaluated with specialized instruments. Additional in situ measurements, such as turbidity, dissolved oxygen, and other physicochemical parameters, were recorded with multiparameter probes and complemented by atmospheric observations using Microtops II and CIMEL photometers. This contribution presents preliminary results, focusing on the evaluation of the quality and reliability of IBIS airborne imagery, as well as advancements in SIF retrieval algorithms. Special attention will be given to the novel capability of estimating spectrally resolved SIF from airborne imagery, as foreseen for the FLEX mission. SIF retrievals will be quantitatively compared with ground-based measurements from FLOX spectrometers, complemented by the assessments of the spatial and temporal consistency of the SIF maps produced. Finally, the potential contribution of these results in the framework of Cal/Val activities of the FLEX mission will be discussed