1. Wellington VAAC Operations during the 2011 Puyehue-Cordon Caulle event
Marcel Roux
Manager, Wellington VAAC
Meteorological Service of New Zealand Ltd

2. Focus Areas Ash detection
Data exchange, collaboration and co-ordination
Confidence levels on the Volcanic Ash Graphic
Image Source:
I’ll be discussing the tools that the Wellington VAAC used when detecting volcanic ash, the different types of data that were at the Forecaster’s disposal and how some of the observational data produced challenging scenarios. The VAAC received pilot reports that resulted in grounding or almost grounding all flights operations in and around NZ. There were also pilot reports that resulted in the CAA having to significantly lower the base altitude of controlled airspace.
The final point deals with how confidence levels could be decided upon in the horizontal and vertical extents. There is still a growing need for flight dispatchers around the world to gain some idea as to the likelihood of a VAAC forecast changing between standard issues.

3. Ash Detection Satellite Imagery Infra-red and visible
Sulphur Dioxide imagery
Laser-radar imagery
Darwin VAAC
This is the list of satellite imagery that was used during the event. Infra-red and visible imagery is accessed via MTSAT, MODIS and GOES W/E. Sulphur dioxide imagery is accessible via the Support to Aviation Control Service website ( sacs) and continues to be a useful alerting tool for areas of possible ash. Callipso lasar-radar imagery was used cautiously since it is not routinely used by forecasters (not a lot of operational experience with the tool).
Multi-Spectral imaging was also applied where possible to aid the forecaster in positioning the most likely area of ash. There were images of very clear ash on MODIS imagery, but there were also ambiguous areas where forecasters had to make judgment calls.
The DARWIN VAAC were kind enough to share multi spectral imagery covering the area well west of the Wellington VAAC, which was useful in alerting the forecasters about approaching areas of ash.
Image Source:

4. Ash Detection Pilot Reports of Ash or No Ash
Routine receipt across NZ and between Australia and NZ.
Reports grounding flight operations
PIREPs became more and more important as the event went on. Particularly when satellite imagery was of little use in determining the areas of visible ash. Routine receipt of PIREPs from Air NZ and other operators (as passed on by the Darwin VAAC) helped the Forecaster paint a more accurate picture of where the most likely area of visible ash was at time step T+0.
Theses are three examples of the pilot reports received from New Zealand domestic operators. The no ash reports were as useful to the Forecaster during this event as the ash reports were.
There was a report that resulted in the VA Forecast being lowered to a threshold altitude that effectively stopped flight operations around NZ for a period of time.

5. Ceilometer and LIDAR CL31 – ceilometer on certain of MetService’s AWSs
2 CL viewing licences.
17 locations around NZ.
NIWA operated LIDAR, located in Lauder
During favourable meteorological conditions, the VAAC Forecaster was able to view Ceilometer data to aid in ash detection. MetService is able to potentially detect ash up to FL250 at 17 AWS sites across the country. A Forecaster was able to view two stations at a time during the Chilean event.
Following the event MetService have acquired an additional 2 licenses from revenue attained from all NZ based airline operators. This means that a forecaster can now view up to 4 stations at one time when attempting to detect ash. The picture below is an example of a MetService operated CL31 ceilometer.
NIWA (National Institute for Atmospheric and Water Research) was also kind enough to pass on LIDAR data from Lauder (located in the lower part of the South Island). This was a valuable tool used by the forecaster when deciding the vertical extent of the ash.
Images Copyright Meteorological Service of New Zealand Limited 2012

6. Pilot Reports Evidence of ash and no ash in satellite imagery
Conflicting Pilot Reports
NO ASH and ASH reports over similar flight routes.
As mentioned earlier the VAAC was able to access a number of pilot reports both over NZ and across the Tasman. However, a challenge that a Forecaster faced was how to deal with reports of ASH and NO ASH over areas that were close together. Across NZ there were reports of both ash and no ash reported along similar flight routes. While the Forecaster found these reports very valuable during the decision making process, the forecast could not be built to take into account every detailed report. The ash was considered very mobile and the areas of ash very changeable.
Image Source:

7. MTSAT Imagery
11 June UTC
This is a good example of a VIS image (to the left) and multi-spectral differencing image (to the right) that the Forecasters used, to determine visible ash as it approached and moved over NZ. While this is a very good image of visible ash, the forecaster was faced with scenarios that were not as clear cut. Other data sources such ceilometer data, LIDAR data and PIREPs became increasingly important in those situations.
MTSAT imagery courtesy Japan Meteorological Agency

8. MODIS Imagery
Ash
Good example of definite areas of ash that the Forecaster was able to use during the observation portion of the volcanic ash graphic. Due to MODIS imagery only covering certain locations at certain times, the Forecaster could not always rely on the imagery for producing definite areas of visible ash.
The imagery was also used to verify past positions of ash and validate dispersion model data.
Ash

9. Data Exchange, collaboration and co-ordination
Civil Aviation Authority (CAA)
Darwin VAAC
Airways Corporation NZ
Air New Zealand Flight Dispatch
This involved the following organisations:
CAA
Handled all media activity during the event
Allowed the VAAC to focus on operations, which proved quite challenging since 60 additional shifts were added to cover the extensive workload that came with this event.
DARWIN VAAC
Provided Wellington VAAC with enhanced satellite imagery over areas west of the Wellington VAAC. This proved useful in alerting the VAAC about approaching areas of ash.
Contacted Darwin VAAC Forecaster to discuss boundaries and levels
Key to consistency
Darwin VAAC passed on Australian PIREP data
Aided the VAAC Forecaster in determining the most likely areas of observed ash
As a result of this event the boundary between the Wellington and Darwin VAAC changed slightly from 160E to 163E. This allowed a better alignment of the NZZO FIR and the VAAC boundary.
AIRWAYS CORP
Pilot reports automatically ingested into our system. Routinely checked by Forecasters upon arrival.
Receipt via or phone.
Air New Zealand
Collaborative relationship helped the Forecaster understand the operational thresholds.
Provided the VAAC with daily reports of ASH or NO ASH (via Airways Corp and ).
Very useful when determining the most likely areas of visible ash
Air New Zealand operates about 520 domestic flights a day
An official procedure is in place that directs the Duty Forecaster to contact the International Flight Watcher directly regarding any PIREP data. The number is monitored 24/7.

10. Data Exchange, collaboration and co-ordination
The flow chart is an example of how data is exchanged collaborated and co-ordinated when an eruption over NZ takes place. The red arrows depict those instances when the VAAC contacts external parties. The green arrows show who the VAA/SIGMET bulletins are sent to. The orange arrows show the path of external information received by the VAAC during VA events.

11. Consistency
Collaboration between the Darwin and Wellington VAACs brought about consistency between the VAA/VAG forecasts.
This is an example of how the VAG matched between the VAACs which proved helpful to flight planners. This example shows a slight difference in the base altitude of the ash along the boundary. The Wellington and Darwin VAAC Forecasters made a joint decision about this based on meteorological reasoning.

12. Possible VAG Confidence Levels
Confidence in the position of lateral boundaries of ash cloud
High = Black
Medium = Blue
Low = Red
Same technique could be used to assess confidence in the vertical extent
After consultation with the Darwin VAAC, a possible way to depict confidence levels would be to create some technique that does not add a significant amount of work on the VAAC and produces a product that would be considered useful during the Flight planning process.
This could be apply to the:
Boundaries of the volcanic ash graphic
Base and tops of the volcanic ash graphic
This could be applied to the T+0 time step along the edges of the polygon. If successful then it could be rolled out to T+6 etc… Instead of assessing the content of the polygon, the boundaries are rather considered and this would alert flight planners as to the likelihood of the edges changing significantly between forecasts.
For the boundaries (as suggested by Darwin VAAC):
High Confidence: An ash/no-ash boundary is discernable* for greater than 2/3 of the length of the polygon edge.
Med Confidence: An ash/no-ash boundary is discernable* for 1/3 to 2/3 of the length of the polygon edge.
Low Confidence: An ash/no-ash boundary is discernable* for less than 1/3 of the length of the polygon edge.
For the vertical extent of the volcanic ash,
This would not increase the workload substantially for the VAAC Forecaster, since he/she are already thinking about this when preparing the ash forecasts.

13. Confidence of Vertical Extent
Objective confidence levels
IR Temp and Sounding vs Lidar, Radar and PIREP
Amount of consistent observations
Image Copyright Meteorological Service of New Zealand Limited 2012
After consultation with the Darwin VAAC, a possible way to depict confidence levels in the vertical could be to develop some objective method which would allow the VAAC Forecaster to assign weighting to various methods for height determination. IR Temp and Sounding versus Lidar, Radar and Pirep. The Lidar, Radar and PIREP data could carry a medium confidence while the IR Temp and Sounding data could carry high confidence.
The proportion of the observations which are consistent with each other could determine the level of confidence.
For example:
If a Forecaster is able to get observed ash data from 3 different sources (either PIREPs, Satellite, Lidar, Ceilometer or SO2 imagery)  that matches within some vertical distance, that could be considered as High confidence.
2 sources matching and 2 sources not matching within some vertical distance could be considered as Medium confidence.
Conflicting observations or no observations could be considered as Low.
Together with Darwin VAAC, we believe it is possible to develop rigorous criteria for decision-making using a set of non-consistent observations.
Image Courtesy of the National Institute of Water and Atmospheric Research

14. Example of Confidence Technique
This is an example of a volcanic ash forecast issued during the Chilean event of last year. There are two levels of ash. The lower level of ash at FL130/FL270 proved problematic for domestic operations across the South Island and resulted in grounding of aircraft.
If the VAAC Forecaster was to employ the technique described above, he/she may decide upon the following. (Go into details on the image). The low level of confidence along the boundaries of the lower ash could be due to the presence of extensive meteorological cloud or the higher ash obscuring the lower level of ash. This image could then alert Flight planners that there is a strong likelihood that the boundaries of the ash at lower levels will change between forecasts.

15. Example of Confidence Technique
This is an example of how the altitudinal confidence may be assessed. If the Forecaster was to receive conflicting reports of the lower ash level being at FL100, it may result it them highlighting that level as low confidence. This would then alert a Flight Planner to the risk that the lower level of ash may change when the ash forecast is updated. This may result in the Flight Planner contacting the VAAC directly to assess whether the level will be lifted or dropped further.

16. Example Confidence Chart
Finally, combining both ideas, an image may be produced that will provide information on the likelihood of the horizontal and vertical extent of ash changing between issues. The Flight Planner would then be able to identify those areas that are most likely to change between forecasts and plan accordingly.
I would encourage discussion to take place around confidence levels and would also like to thank Emile Jansons, Manager Darwin VAAC, for ideas and assistance in this area.