Tropospheric Observing System for the Investigation and Management of the Environment – VOLTIGE

The VOLTIGE project is based on ultra-light flixed-wind aircraft which have been equipped with the Paparazzi open-source autonomous navigation system (http://paparazzi.enac.fr/). Inertial navigation allows autonomous control even during fog events and radio communication relays scientific data to the ground-control station for real-time monitoring during the flight. The total take-off weight of the RPA is less than two kilograms with a scientific payload up to 200 g. Sensors include pressure, temperature, relative humidity, broadband solar flux, turbulence, and cloud extinction. An acquisition system centralizes the collection of the high-frequency data and relays a subset of the data to the ground-station via the autopilot. As payloads are relatively small, each RPA is equipped with modular payloads based on a particular science focus. Three science-oriented platforms were developed for the VOLTIGE project: solar fluxes, turbulence and cloud measurements. Each platform was also equipped with meteorological sensors. Unique flight plans have been developed such that the platforms fly simultaneously to study the evolution of the fog event. In addition, the autopilot incorporates the sensor data to automatically change flight trajectories based on a particular set of atmospheric conditions.

Over 160 flights and more than 35 flight hours have been conducted as part of the VOLTIGE project. Five different platforms were flown during the project, including a flying-wing with four control surfaces to separate elevator and aileron controls in order to reduce the pitch angle envelope and improve turbulence and albedo measurements. Four aircraft flew simultaneously, each with a different flight plan and science payload. The sensor measurements were used by the autopilot to adapt its flight based on given atmospheric conditions. A few flights were conducted during dissipating fog events, but it general we found it difficult to coordinate the forecasting of fog events with the limited time-window allowed by airspace restrictions.

Nonetheless, vertical profiles from the VOLTIGE flights have been compared to Météo France forecast models, and the results suggest that forecast models may be improved using high resolution and frequent in-situ measurements. The Basse Couche Campaign (BAC+) was initiated as a collaborative agreement with the military’s flight school (French Army Light Aviation; EALAT) to conduct regular UAS flights in the Landes – a region known for its fog. BAC+ provides a first-step towards deploying small RPAS in an operational network at Météo France. In addition, the VOLTIGE project has been a key element in developing collaborations focusing on the use of RPAS in atmospheric science with other laboratories in the Toulouse region as well as at the European level.

The VOLTIGE program engaged many students over the course of the project, including two master’s students, numerous internships and training courses. The École National de la Météorologie now includes the development and sensors integration of RPAS as part of its academic curriculum.

The VOLTIGE project has been a key element in developing the first UAV program for atmospheric research in France as well as establishing numerous collaborative efforts between research institutes in Toulouse and throughout Europe.

The goal of the VOLTIGE project was to show the feasibility of deploying lightweight UAS for fog studies using an intelligent, multi-observational approach. While technical in nature, the project has resulted in a number of reports and publications; and has been visible at the international, national and local levels. The main highlights include articles in Metéo et Climat, Le Journal CNRS, and INP Toulouse Communique, which have garnered public attention of the civilian use of RPAS; and the presentation of results at national and international conferences.

The proposed project aims at developing a novel in-situ observing system to expand measurements of the Earth’s atmosphere with a focus on boundary layer processes. VOLTIGE (Vecteurs d’Observation de La Troposphère pour l'Investigation et la Gestion de l'Environnement) is a French word for aerobatics or stunt flying; and the acronym translates to ‘Tropospheric Observing System for the Investigation and Management of the Environnement’. To date, radiosondes are the only routine in-situ means of profiling the earth’s atmosphere – and with a very limited set of sensors (temperature, relative humidity and pressure). To address the scientific and technical challenges related to observing the atmosphere, the proposed project is centered on unmanned aerial systems (UAS) for scientific and civilian applications.
Atmospheric research and forecasting models have long suffered from a gap between ground-based and satellite-based measurements of the atmosphere. As a consequence certain atmospheric phenomenon, such as aerosol-cloud interactions, remains one of the largest uncertainties in understanding climate change. On regional and shorter time scales compared to climate change, adverse weather conditions also pose risks to the transportation industry, particularly when visibility is reduced. Future improvements in numerical weather prediction and climate simulations rely on systematic observations of atmospheric parameters to characterize the vertical dimension and to improve integration of in-situ measurements and satellite observations.
VOLTIGE strives to fill a niche for UAS by developing autonomous profiling capability and coordinated observations – introducing a re-usable sonde that contains a variety of sensors to address a particular science theme (e.g., fog life cycle). This project has two major objectives: 1) increase our scientific capacity to observe the atmosphere and surface of the Earth; and 2) engage students to the recent technological advances in meteorology and aeronautics.
Of specific interest in VOLTIGE, the proposed project builds on existing observational capabilities to observe the major parameters related to fog cycles via an integrated network of sensors. The occurrence of fog events are of great concern for airport operators and air transport companies. However, forecasting of fog events is still a major challenge because numerical simulations lack sufficient information to predict or reproduce fog events using classical meteorological models. Most fog studies are limited to ground-based measurements that utilize remote sensing techniques to explore the vertical structure. Currently, in-situ airborne measurements of fogs are only possible with balloons and the applications of balloons for fog research have been scarce.
VOLTIGE develops the tools to build an observational capability that extends beyond the specific science applications proposed here. Hence, by coupling novel technology with innovative science, this project engages a future generation of scientists and engineers at the École Nationale de Météorologie (ENM) and the INP-École Nationale de l’Aviation Civile (ENAC). The application of VOLTIGE in an operational network will be integral to the education of students at ENAC and INP-ENM. These low-cost systems may be deployed for eventual operational use for meteorological forecasts and surveillance of toxic plumes in case of industrial accident or volcanic ash plume. If successful, this project will further establish lightweight UAS as viable and cost-effective observing platforms for environmental sciences.