The availability of highly integrated laser and optics technology offer the prospect of increased aircraft Air Data System robustness in adverse conditions. Indeed, although critical, the system is subject to hailstone, icing, corrosion, bird collision, passenger stairs mishandling. Thus the optics technology offers the capability to improve the operational capacity and safety of the air transport system. DANIELA aimed to carry out research and development as well as technology maturity improvement to prepare the installation on new airliners of a fully non intrusive Optical Air Data System (OADS).
Thus the project focus was on:
- validating the capability of the system to measure the parameters in all flight conditions;
- addressing the main issues coming from the use of signal back scattering instead of well known pressure measures. Atmosphere particle dissemination studies will be performed, and OADS system will be evaluated in a worst case i.e. high altitude un polar conditions;
- investigating mature dedicated technology improvement in laser sources and optical functions integration glasses are the key technology to reach commercial air transport requirements and ensure a European source for optical ADS, along with dedicated signal processing schemes. Resistance of side mounted OADS glasses to dust, ice or sand as well as any atmospheric erosion were evaluated during representative tests in wind tunnel;
- evaluating the new temperature measurement principle that allows replacement of the intrusive TAT probe. Future generation airliner studies have already set the main driver for a competitive aircraft.
DANIELA aimed to push integration a step beyond NESLIE (FP6) demonstrator to fully validate the OADS concept with regards to future commercial air transport needs. The output of the project is validated technology that enable the introduction of OADS in future airliners (around 2015) and secure the certification process of such aircraft.
The aim of the DANIELA (Demonstration of ANemometry InstrumEnt based on LAser) project was to prepare the operational use of a flush mounted ADS (Air Data System) built around a three axis Doppler LIDAR function as a primary air data channel on civil aircraft, and to assess optical concepts for the measurement of temperature and density to complete the ADS.
The availability of highly integrated laser and optics technology offer the prospect of increased aircraft Air Data System robustness in adverse conditions. Indeed, although critical, the system is subject to hailstone, icing, corrosion, bird collision, passenger stairs mishandling. Thus the optics technology offers the capability to improve the operational capacity and safety of the air transport system.
The project was organised into work packages resulting in:
- Survey on worldwide particles distribution in the troposphere for a better assessment of optical measurement availability (based on satellite observations and on ground observations);
- Design of a highly performing mock-up in adverse conditions (very low concentration of particles);
- Research and development of on board laser using innovative technologies;
- Development of a complete functional mock-up;
- Flights test in adverse conditions (arctic region);
- Studies and evaluation of promising technologies in temperature measurement;
- Consortium management.
The duration of the project was 36 months.
A flight test campaign to Africa was successfully finished. After that, the aircraft was restored into its original configuration. Flight test data has been recorded and distributed, together with explanations on its contents and use of the data. An elaborate overview of all test flights can be obtained from the project coordinator. Post-flight analyses shows that almost all required atmospheric phenomena have been encountered. The ones not encountered, were simply not available during the flight test periods.
Flight test engineers have taken part in the some flight tests. The recorded data (LIDAR and aircraft references, videos, in-flight notes from pilots and DANIELA operator, meteo forecasts) have been analysed and reported. Based on that, signal processing has been adapted and performance assessment is done.
The use of laser technology is an alternative solution to improve the operation by the main airframers as it is not affected by icing/rain environment and no programmed maintenance operation is foreseen. Even in the case laser technology is unable to provide all parameters at an early stage, a partial implementation using three axis velocity is envisaged as that enables removing the most exposed external probes (AOA/SSA and PITOT).
Many varieties of LIDAR systems have been studied to measure the atmospheric temperature. Some of these systems have reached a high degree of maturity for long-range ground-based measurement. However, various systems have not been described in this state-of-the-art study of optical methods for temperature measurement. This is because their setup or their physical principle is not well suited for airborne application. An example is LIDAR using fluorescence of metallic atoms, as these are not present at flight altitude.
Various techniques useful for airborne application have been studied in the project. Optical methods usable to measure air temperature are all based on molecular scattering. When light is scattered by molecules, the photons generate the so-called Cabannes line of Rayleigh Scattering. Among the most promising methods for airborne remote optical temperature measurement, are:
- the Rotational Raman technique;
- Rayleigh technique.
Rotational Raman technique:
The Rotational Raman technique which is based on the temperature dependence of inelastically scattered light by N2 and O2 in the air. Temperature measurement based on Raman Scattering shows that accurate measurements can be achieved in with reasonable laser power. This method has various advantages. The main technological difficulty lies in the realisation of the required optical filters.
Rayleigh Scattering is one of the major physical mechanism that has been studied in literature since both backscattered intensity and spectral width can give access to atmospheric temperature.
Both principles (Rayleigh Scattering and Raman Scattering) present theoretical and technological advantages and disadvantages, and both offer specifically optimised subsets of measurement principles, both have been analyzed in the DANIELA project.
Innovating for the future (technology and behaviour): A European Transport and Innovation Policy