Volcanoes and Aviation: Part 2/2

Since 1900s volcanic ash have disturbed air travel and posed a threat to aviation. Many existing techniques that were used by volcanologists, to study volcanoes and their characteristics, were developed to support the aviation industry. I intend to discuss some of these methods in this post.

Seismic Monitoring

The term ‘seismic’ refers to earthquakes, seismic monitoring monitors the earthquakes that occur because of volcano becoming restless. Seismic activity under the volcano increases before an eruption because magma and hot gases need to force their way through the Earth’s crust. Most of the volcanic earthquakes are less than magnitude level 3 and occur less than 10 km beneath the volcano.

Various seismometers are place within the range of 20 km of the volcano to monitor ground vibrations. The locations of these seismometers are decided strategically to pick up small earthquakes of magnitude levels 1 or 2. Computer technology has enabled today’s scientists to predict eruptions more precisely by seismic monitoring technique and determine real time changing characters of the volcanoes.

Satellite Imaging

Satellite imaging plays a critical role in detecting volcanic eruptions and following the volcanic ash clouds. Satellite imagery consists of high-resolution photographs of the Earth taken from satellites that orbit our planet.

There are several types of satellites, each one having a different resolution and capabilities. Geometric resolution and Ground Sample Distance (GSD) refers to satellite sensor’s ability to image a part of the Earth’s surface within a single pixel. The highest resolution satellites are used primarily for military and intelligence i.e. Ground Sample Distance available to US Department of Defence is less than a centimetre and the satellite has the capabilities of Real Time (live) Imaging. GSD civilian access is restricted to 0.5 metres and no live coverage is available. Geo-Eye, Digital-Globe, SPOT Satellites, Rapid-Eye and EROS are few examples of civilian accessed satellites orbiting our planet Earth.

Many disadvantages of using satellite imagery exist and one of them is the speed of relaying information to different places. The Earth’s surface is enormous and therefore the database is very large, thus image processing is very time consuming. Weather conditions also affect the quality of the image. Moreover, satellite images are not placed in the public domain, only certain license holders can access these images.

Despite these and other disadvantages, satellite imaging plays a fundamental role in identifying volcanic eruptions and tracking ash clouds. Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite detected re-suspended ash of Eyjafjallajökull Volcano on May 26, 2010.

Hydrologic Monitoring

Hydrologic Monitoring of volcanoes involve surveyors who examine lakes and rivers for sediment erosion and deposition. Through the data observed and collected scientists can better learn the characteristics of the specific volcano and can even predict future eruptions.

Lahar-detecting system has been developed to monitor debris flows. This system provides an opportunity for accurate warnings for people living downstream. Hydrologic monitoring provides hazard information and develops better understanding of the hydrologic processes involved in the devastation and recovery of affected areas. This information is used to investigate variables affecting the stability of streams and fluid dynamics of flows that transport high sediment loads.

Lightening Detection and Gas Flux

Lightening detection is currently being used in New Zealand and some northern regions of US. Lightening in the ash cloud is generated by volcanic ash cloud’s electrical phenomena. To detect the lightening, several lightening detecting sensors are placed which feeds the World-Wide Lightening Location Network (WWLLN). This data is used to alert key action centers via emails about suspicious lightening. Currently, only few regions have ‘active’ alerts as the system is still under development.

Gas Flux is a technique to study the volcanic ash clouds. This is of global significance because carbon dioxide emissions contribute to greenhouse effect. Flux measurements are useful in hazard prediction and provide insight into eruptive mechanisms. This method is currently researched upon by scientists.

FREENOX

Spanish company, Aero Engineering, developed a new type of high bypass turbofan engines which will revolutionize the concept of aircraft engines. The claimed advantages over conventional turbofans include optimal weight/thrust ratio, improved combustion, reduce fuel consumption, decreased environmental and acoustic pollution, can reduce 80% of nitrous oxide emissions and the engines are foreign object damage proof (i.e. volcanic ash). Some of patent technologies shared by Aero Engineering on their website are:

  • Endothermic Reaction System (ERS) which monitors the thermal conditions
  • Engine System Manager (ESM) is the central processing unit for the system
  • NG Combustion Chambers which is a new design of combustion chambers
  • High Performance Fan Sky Lift (HPSL) which is a new intake fan design
  • FAPS which is an innovative propulsion system
  • Central Compression Unit (CCU) is responsible for air compression
  • Advanced Internal Exhaust Nozzle (AdIEN Turbine) which is a revolutionary turbine and nozzle integrated system

ERS can improve fuel combustion at different stages of the flight by producing activated oxygen. The whole system is governed by ESM which requires a simple input from the pilot such as start, take off, cruise and landing. Subsequently the ESM module carries out all the other necessary functions and optimal mixtures of activated oxygen, compressed air and fuel, considering temperature, altitude and pressure. CCU is an electrical system installed at the rear inside of the fuselage depending on the configuration and it is powered by electrical generators integrated within the reactors. CCU provides the necessary air pressure required for ERS to operate. Air is compressed and stored in CCU before getting distributed to each engine.

During cruise mode, CCU adds the necessary propulsion to the aircraft when ERS reduces power to the engines. Hence, reducing fuel consumption and therefore reducing the carbon dioxide emissions.

This system is still under development and testing with no publicized release date.

CALPUFF

CALPUFF is an integrated modelling system with pre-processing and post-processing programs. Three main modules of modelling system are:

  • CALMET – three-dimensional metrological model
  • CALPUFF – air pollution dispersion model
  • CALPOST – post-processing module.

CALPUFF model is Lagrangian dispersion model designed to simulate dispersion of air pollution over long distances. The advantages of CALPUFF include different granulometric classes, time dependent emission and meteo data, dry and wet deposition, buoyant area source, and domains from tens of metres to hundreds of kilometres from the source. One of the major features of CALPUFF is the capability of treating the case of very hot area source by solving three fundamental equations of momentum, energy and mass.

Validation of CALPUFF code can be achieved by performing well-known tests and comparing with observed data. CALPUFF is used to model Etna Volcano which erupted in July 2001. Results are promising and we can conclude that it will be a very capable model of real-time forecast of volcanic ash dispersal.

Ground-based Real Time Monitoring (GRTM)

Ground-based Real Time Monitoring (GRTM) of eruption clouds is a technique used in Kagoshima University of Japan. This technique is used to study the volcanic clouds and provide long distance warning. Long-time automatic observation is achieved by interval recording methods.

Camera lenses used for recording have Neutral Density (ND) and Infrared (IR) filters. Advantages of NIR observation include detection of vegetation damage and hot anomaly, distinguished aerosols, not obscured by sea haze and good resolution.

One such GRTM network is installed to monitor Mayon Volcano located at Lignon Hill Observatory. The recording cameras and the Network Attached Storage (NAS) are further connected to another hub, which transfers the data to PHIVOLCS Telemeter Network, then to the internet and finally to Kagoshima University. The video is recorded and sent back to NAS every 10 minutes. The complete system is up and running since 2004. GRTM associates believe that this system is important for aviation safety, disaster prevention and avoidance of ash.

Active Tracer High-resolution Atmospheric Model (ATHAM)

Active Tracer High-resolution Atmospheric Model (ATHAM) has potential to be used for air traffic safety. Model can simulate various processes ranging from dynamics, turbulence, micro-physics, aerosol and gas scavenging. ATHAM can simulate precise volcanic eruptions which in turn provide good predictions to help pilots make better decisions. This system is being worked upon in University of Cambridge, UK.

Ground-based Infra-Red Detection (G-bIRD)

G-bIRD is an initiative of Australian companies, Tenix and CSIRO, and the project is multi-million dollar investment. It claims that it will provide early warnings to pilots and related organisations regarding volcanic ash and sulfur dioxide clouds. Early tests of this system have been conducted in Hawaii and Guam. Dr. Prata of CSIRO Atmospheric Research said:

“CSIRO is really excited to be working with Tenix to deliver this Australian innovation for new global markets with the impact of enhancing safety and reducing costs to the airline industry. The G-bIRD project has built on the strengths of both organisations to develop something of tremendous value to the world aviation industry.”

Volcanic Ash Advisory Center (VAAC)

Volcanic Ash Advisory Center (VAAC) is an establishment of a group of experienced individuals who are responsible for organizing and interpreting data on volcanic ash. VAAC was setup in 1990s by International Civil Aviation Organisation (ICAO) as part of the International Airways Volcano Watch (IAVW). There are nine Volcanic Ash Advisory Centers in the world, each one responsible for their own geographical region.

The main purpose of these nine centres is to gather information from observatories, satellite images and pilot reports on volcanic ash. This information is then analysed by professionals and action plan is devised. These plans are then issued to airlines, meteorological watch offices, area control centres and neighbouring volcanic ash advisory centres.

London Volcanic Ash Advisory Centre is based at the Met Office and runs the NAME III dispersion model which helps to forecast the spread of volcanic ash clouds. The parameters inserted in the model includes location, start time, release height (top and bottom of the cloud). After 15 minutes, output is achieved which is in a graphical format and shows the expected ash concentrations over a large area. Met Office also uses satellite detection technique to track volcanic clouds.

High Temperature Thermal Barrier Coatings (TBC)

A coating system that reduces the temperature and increases the component life.  Thermal barrier coatings (TBCs) are generally a combination of multiple layers of coatings, each layer having a specific function and requirement.  The top layer provides thermal insulation and consists of ceramics, with low thermal conductivity, typically Zirconia.  The ceramic insulating layer is deposited on the substrate alloy, which in our case is the turbine blades. During the ceramic coating deposition, a thermally grown oxide (TGO), usually aluminium oxide, forms on the interfaces. The TGO binds the ceramic layer to the bond coat and bond coat to the substrate.

Turbine blades and vanes are designed to provide active cooling to the entire system of turbine and TBC takes advantage of this cooling system to provide effective protection. The blade, coated with TBC, is actively cooled by cold air from the compressor. The cold air is directed through the internal cavity of the blade to remove the heat.

Examples include a Boeing 757, which is equipped with Pratt & Whitney’s PW2000 turbofan engines. Tests performed by Pratt & Whitney shows significant temperature reduction by using TBC. The PW2000 turbine blade has a 125 µm thick Zirconia based TBC which was deposited by Electron Beam Physical Vapour Deposition (EB-PVD) technique. The tests resulted in 139°C reduction in the local hot spots.

Nitin Padture’s Formula for TBC

A new research has discovered that a new class of high temperature ceramic coatings could offer jet engines special protection against volcanic ash and sand damage. The researchers at the Ohio State University tested two coatings that were originally developed to keep airborne sand from damaging jet engines, and found that the coatings also resist damage caused by ash deposits. When the Icelandic volcano Eyjafjallajökull erupted in April 2010, it blasted clouds of silicate ash.

Researchers took samples of the ceramic coatings on pieces of metal, and coated them with ash from the Eyjafjallajökull eruption. Then they heated the samples in a furnace to simulate the high temperatures created in a jet engine. They experimented with a typical jet engine coating and two sand-resistant coatings. One was Padture’s formula, containing zirconia and alumina, and the other was a commercially available new formula based on gadolinium zirconate.

Temperatures inside the engine can reach up to 1500°C, and ceramic thermal-barrier coatings insulate metallic engine parts from that heat. The ingested ash melts onto the coating and penetrates the coating. Upon cooling, the molten ash forms a brittle glass that breaks off, taking the coating with it.

In the test, the ash badly damaged the typical coating, while coatings made of Padture’s formula and the gadolinium zirconate formula retained their overall structure. Looking at cross-sections of the samples, the researchers saw why the molten ash had penetrated through the pores of the typical ceramic coating all the way to its base. But in the other two, the molten ash barely penetrated.

Pores gave the coating its strain tolerance. They made room for the coating to expand and contract as the engine heated up while flying, and as it cooled after landing. When all the pores are plugged with ash, the coating can’t adjust to the temperature anymore and it breaks off.

On the sand-resistant coatings, the ash filled the pores only near the surface. Chemical analysis revealed that the ash reacted with the alumina in the first coating to produce a thin layer of the mineral anorthite below the surface, while on the gadolinium zirconate it produced a layer of the mineral apatite. The chemical reaction stops the penetration of the ash into the coatings. The unaffected pores allow the coating to expand and contract.

Concluding Remarks

The methods mentioned in this article are the major ones that are working together to provide safe air travel. However, there are several other methods and technologies being researched upon that I didn’t mention.

*list of information sources is available on request

Note: I recognize and appreciate the respective owners of this information and I do not intend to take credit for someone else’s work. This post intends to bring the useful information together for the avid readers.

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