Proceedings of the 44th European Microwave Conference
The X-WALD Project: Towards A Cleaner Sky M. D’Amico 1, S. Lischi 2, A. Lupidi 2, F. Cuccoli 2, F. Berizzi 2, S. Placidi 3, F. Milani 4 1
DEIB, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy
[email protected] 2
RaSS-CNIT, Galleria G.B. Gerace 18, 56124 Pisa, Italy
[email protected],
[email protected],
[email protected],
[email protected] 3
Metasensing BV, Huygensstraat 44, 2201DK Noordwijk, The Netherlands
[email protected] 4
IDS Ingegneria Dei Sistemi, Via Flaminia 1068, 00189 Rome, Italy
[email protected]
Abstract— In the last years, the Cleansky EU programme has been promoting research towards new concepts in aircraft and avionic design in order to enhance sustainability and flight security. The X-WALD project, in the framework of Cleansky programme, focuses on the validation of algorithms for the evaluation of hazards coming from meteorological conditions encountered in flight. The validation will be performed exploiting both data coming from an advanced polarimetric weather radar simulator and data collected by an aircraft during an experimental campaign. Keywords—Cleansky; airborne radar; radar polarimetry; radar simulation; validation.
I.
INTRODUCTION
Civil airplanes and military transport aircrafts are usually equipped with avionic weather radars (AWR) [1]. In the past, the first function of avionic radar (in civil aviation) was related with autonomous navigation. Nowadays, current AWRs allow having different functionalities on detection of dangerous weather phenomena (Fig. 1). Typical and possible methods and systems so far developed, both for ground-based and for airborne applications, to detect dangerous weather zones and to be implemented in future weather radar systems are: (1) conventional radar, that is, non-coherent radar, which is able to measure radar reflectivity only, ignoring polarization features of the signal; (2) coherent (Doppler) radar that can measure Doppler spectrum parameters; (3) polarimetric radar, which takes into account signal polarization to improve system performance characteristics. The highest potential can be obtained by the Doppler-polarimetric radars that combine both Doppler and polarimetric diversities to improve detection performances. Single polarization radars permit to detect only the intensity of the meteorological phenomenon, which is anyway, in case of high values, obviously linked to harsh and dangerous conditions, like hailstorms and turbulence. Polarimetric radars can provide more refined information on the type of precipitation once the model of specific hydrometeor (rain, snow or hail)[2] is known. Polarimetry is typically used in meteorological ground radars for weather monitoring and nowcasting, but so far it is not used in avionic commercial radar apart from some experimental systems. In
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this work we present the X-WALD project, whose objective is to explore, through a campaign of experimental measurements, the potentials of Doppler-polarimetric radars in civil aviation. II.
THE CURRENT SCENARIO
As stated above, at the moment polarimetry is not exploited in airborne commercial radars. Standard frequency bands for airborne weather radar are X and C bands while ground-based radar normally uses S band and C band [3]. Two manufacturers, Honeywell [4] and Rockwell Collins [5], dominate the weather radar market in air transport. These radars, but in general all current commercial avionic radars, only operate with single polarization. Honeywell RDR-4B and RDR-4000 are multifunctional airborne radars with digital signal processing aimed to hazardous weather detection and avoidance, classified as weather radar with forward-looking windshear detection capability; the former is designed particularly for observing weather up to 320 NM, windshear up to 5 NM and turbulence detection up to 40 NM, whereas the latter presents an evolution of technology with 3D volumetric scanning of the atmospheric phenomena, evaluating not only the conditions on the flight path but in the forward volume, useful for avoidance options up to 320 NM, pulse compression and advanced ground clutter reduction. Rockwell-Collins WXR-700X and WXR-2100 are two solid-state weather radars, the former utilizes Doppler methods to detect turbulence and windshear, whereas the latter, the WXR-2100, is a competitor of the RDR-4000 and it tends to evolve in the direction of Integrated Surveillance System (ISS), trying to integrate the transceiver section beyond the antenna, with the aim of decreasing the losses and increasing sensibility. It uses a multiscan technique which enables scans at slightly differing elevation angles and provide over-the-turbulence scan up to 40 NM. It implements fully automatic operations, TWS thunderstorm assessment up to 40 storm cells and Flight Path Hazard Assessment.
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of great importance to extensively test signal processing and trajectory optimization algorithms. Obviously, algorithm performance analysis results and its implementation on an EFB are strictly dependent on the reliability of the polarimetric radar simulator. In this context, the availability of real data in a wellmonitored scenario would be of great importance to test the quality of the simulator as well as the capability of the algorithms. The X-WALD project aims to give a concrete answer to the above problem. IV.
Fig. 1. Downburst, wind shear, hail, icing… X-WALD focuses on weather hazards for aviation safety.
Existing airborne polarimetric radars are mainly used for research purposes, like NASA Airborne Rain Mapping Radar (ARMAR) [6], to remote sensing the weather phenomena, without supporting flight hazard assessment. This radar operates at 13.8 GHz with four-channel dual-linear polarizations (HH, VV, HV, VH) and a bottom mounted antenna working in cross-track direction. It includes Doppler and brightness temperature measurements. ARMAR can obtain a great number of independent samples by using frequency diversity, transmitting up to four slightly different frequencies. In Stepped Frequency (SF) mode ARMAR is coherent, providing Doppler information. For situations in which a high accuracy in Doppler measurement is necessary, the antenna can be pointed at nadir rather than scanning, allowing a substantially larger dwell time and improved Doppler resolution. III.
THE CLEANSKY FRAMEWORK
In the framework of CLEANSKY Joint Undertaking (JU) European program and specifically in the Clean Sky Systems for Green Operations (SGO) Integrated Technological demonstrator (ITD), the use of a polarimetric avionic radar has been proposed in the Management of Trajectory and Mission (MTM) study to have more precise information about not forecasted weather phenomena. The goal is to optimize the skipping trajectories in order to minimize the noise pollution and emissions in each flight phase of the airplane. To this purpose, two projects, namely CLEOPATRA and KLEAN, have been sponsored by the JU-SGO for developing an avionic polarimetric radar signal simulator (CleoSim) and the implementation and testing of polarimetric signal processing (AWR processing (AWRP), AWR post-processing (AWRPP)) and trajectory optimization algorithms (developed by Selex Galileo, now Selex Electronic System: SES) on an EFB (Electronic Flight Bag), respectively. An EFB is an electronic display system designed to replace the traditional pilot flight bag and to reduce or eliminate the need for paper and other reference materials in the cockpit. In the JU-SGOMTM activity, the use of a polarimetric radar simulator has been chosen because of the unavailability of the avionic commercial and/or experimental polarimetric radar among the JU-SGO members and by the difficulty of finding commercial systems. The simulator has the advantage to generate any kind of weather phenomena scenarios, which is
THE RADAR SIMULATOR (CLEOSIM)
During the CLEOPATRA project [7] a new airborne radar simulator was developed (CleoSim), that combines the description of the meteorological scenario at mesoscale level (typical of the environment simulators) with the capability of generating accurate time series of raw signals received by the sensor (typical of the microphysical simulators). The simulator generates a virtual meteorological environment, simulates the transmission of the electromagnetic pulses, and solves the monostatic radar equation to produce a stream of synthetic I&Q samples. The meteorological environment focuses on significant weather hazards for aviation safety (ice crystals, hail, heavy rain, fog, wind shear, turbulence… ) as well as non-threatening weather events which could however impact the airborne weather radar performances (e.g. large scale stratiform rain). The meteorological environment is generated through Harmonie, a limited-area mesoscale weather model that is actively being developed by the HIRLAM/Aladin consortium (http:/www.hirlam.org), based on existing weather models and cloud-resolving models. It accepts the input of a suitable set of high-level parameters describing the scenario of the weather onset. The model provides information (at mesoscale level) about intensity, type of precipitation, spatial distribution, etc. and in particular: 3-D field of 3D wind speed components; 3-D field of rainfall rates and/or snowfall rates and/or hail fall rates and characterization of the water and ice content of the clouds; 3-D field of the main meteorological parameters (air pressure, temperature and humidity, etc.) (Fig. 2).
Fig. 2. 3D image of an example of an extreme weather event simulated by CLEOSIM.
Starting from the parameters available from the meteorological model, microphysical quantities like particles'
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size distribution and shape are derived. The meteorological resolution volumes are filled with hydrometeors of different nature and size, which are randomly placed inside the volume itself. The received signal (I&Q) is calculated as the superposition of the contributions coming from all the hydrometeors present in radar resolution volume. The effects of the characteristics of the radar sensor (installation, frequency, power, antenna polarization and directivity function, sampling & scanning strategy, pulse length and repetition frequency, etc.) as well as the effects due to aircraft attitude and motion (pitch, roll, yaw, altitude, velocity vector, etc), and the possible presence of ground clutter, are all taken into account (Fig. 3). Once the radar equation has been solved for the current configuration of the scatterers, their position is updated for the next pulse, taking into account their terminal vertical fall speed and the presence of wind as well as the aircraft position.
V.
THE KLEAN PROJECT
The KLEAN project (whose architecture is shown in Fig. 4) aims at developing a custom knowledge-based EFB (Electronic Flight Bag) (Fig. 5) with SW packages implementing Advanced Weather Radar Post-processor (AWRP) and QAI (Quasi-Artificial Intelligence) agent algorithms for green trajectory optimization (reduction of CO2 and NOX emissions as well as noise pollution). The EFB includes also an ad-hoc Graphical User Interface (GUI) for output presentation and pilot interaction and custom I/O interfaces to radar processor, external sensors/systems/database and the Mission/Flight simulator. The main KLEAN specific objectives can be summarized as follows: EFB selection platform and purchasing, SW integration and refinement of AWRP algorithms, SW integration and refinement of QAI agent algorithm, design and implementation of a GUI interface for result display and control , design and implementation of a few I/O interfaces for the AWRP, for the Mission/flight simulator and for the internal/external sensors/system/database.
Fig. 4. KLEAN architecture scheme Fig. 3. CleoSim computes the I&Q signals from the synthetic meteorological scenario, includind the effect of ground clutter and system noise.
Fig. 5. The Nexis EFB used in KLEAN
VI.
THE X-WALD PROJECT
As stated, the main objective of the X-WALD project is to plan and run ad hoc measurements finalized to test, validate and optimize: 1) the CleoSim radar signal simulator; 2) the
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TABLE I.
radar signal processing and weather classification algorithms implemented on an EFB in the KLEAN project; 3) the EFB GUI interfaces for the advanced display of weather classifications and decision-making advices developed in KLEAN.
MAIN RADAR SENSOR CHARACTERISITCS
Parameter Frequency
Value Adjustable from 9.45 to 9.75 GHz
Transmitted power
5W
To achieve this goal, the following specific objectives are aimed at: 1) X-band polarimetric radar overview, selection and acquisition. The radar must be suitable to be mounted on airborne platform for gathering data in presence of weather events in compliance with the JU-SGO goals; 2) planning the ad hoc measurement campaign in well-monitored selected scenarios; 3) experiments conduction and data acquisition; 4) validation, optimization and SW refinement of the avionic polarimetric radar signal simulator (CleoSim); 5) validation and optimization of the EFB weather radar signal processing and trajectory optimization algorithms (KLEAN project); 6) refinement of the EFB GUI in accordance with the new needs resulting from the experimental data analysis; and 7) EFB SW refinement and implementation to a level TRL5 (Technology Readiness Level 5).
Pulse Duration
13.33 μs
PRF
2.5 kHz
As far as the experimental site is concerned, a site in the Netherlands has been selected; the first measurement campaign will be carried out in September/October 2014, when intense, convective rain events are frequent. A second experimental campaign will take place around December 2014, when stratiform rain events are typical. The experimental radar system needs to be installed on the nose of the aircraft in a forward looking configuration. Therefore, the TB10 Tobago single 180 HP engine of the French company DAHER-SOCATA[8] has been suggested as a valid aerial platform, with the possibility of installing remote sensing sensors on the wing tip (Fig. 6). Concerning the sensor, a compact fully-polarimetric antenna solution, a Pulsed-FM architecture operating at X-band is in development by the Dutch company Metasensing [9]. The preliminary characteristics of the radar sensor are summarized in Table I.
1 MHz
Compression Factor
13.33
Min operational range
2 km
Max operational range
60 km
Min range resolution
150 m
Transmitter polarization
Pulse to pulse H/V
Receiver polarization
Simultaneous H/V
Antenna type
Parabolic reflector
Half Power Beamwidth
5.97º
Cross-Pol insulation
> 25 dB
Elevation operating range
± 6º
Azimuth scan range
± 60º
Antenna scan speed
Up to 30 º/s
Receiver sensitivity
13 dBZ (SNR=0dB @ 60km)
Linear dynamic range
> 80 dB
MDS
-114 dBm
Some modifications to the related parameters may occur. ACKNOWLEDGMENT The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) for the Clean Sky Joint Technology Initiative under grant agreements n. 271847 (CLEOPATRA), n. 306927 (KLEAN) and n. 619236 (X-WALD). Content of this paper reflects only the authors’ views. Clean Sky JU and European Union are not liable for any use that may be made of the information contained therein. REFERENCES [1]
[2]
[3]
[4] [5] [6] Fig. 6. Tobago TB10: twin engine aicraft with the nose pod option installed.
Chirp Bandwidth
[7]
[8] [9]
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F.J.Yanovsky, “Airborne Weather Radar as Instrument for Remote Sensing of the Atmosphere”, Proceedings of the 3rd European Radar ConferenceManchester, UK., September 2006. J.M.Straka, D.S. Zrnic´, A.V.Ryzhkov, “Bulk Hydrometeor Classification and Quantification Using Polarimetric Radar Data: Synthesis of Relations”. Journal Of Applied Meteorology, vol. 39, pp. 1341-1372, 2000. F.J.Yanovsky, “Recent Researches in the Field of Weather Radar at the NationalAviationUniversity”, MRRS-2008 Symposium Proceedings. Kiev, Ukraine, September 2008. Honeywell Aerospace, “IntuVue RDR-4000™ Advanced Weather Radar”, Phoenix, Arizona, September 2008. Rockwell Collins, “WXR-2100 MultiScan™ Weather Radar”, Cedar Rapids, Iowa, September, 2007. S.L. Durden, E. Im, F.K. Li, W. Ricketts, A. Tanner, W. Wilson “ARMAR: An Airborne Rain-Mapping Radar” Journal of Atmospheric and Oceanic Technology, vol. 11, pp. 727-737, 1994. G. Amisano, C. Capsoni, M. D'Amico, M. Bandinelli, F. Milani, J. de Vries, J. Barkmeijer, E.Itcia, JP.Wasselin, “CLEOPATRA: a Novel Approach to Airborne Radar Simulation”, Radar 2012, Glasgow, UK, pp. 1-6, October 2012. http://www.tbm.aero/ www.metasensing.com/
