NASA Langley Research CenterDEVELOP Program, South Pacific Oceans Team

www.develop.larc.nasa.gov Hampton, VA 23681

Utilizing GNOME and ArcGISfor Pumice Raft Trajectories: A Users Guide

Revised July 25, 2013

ContentsBackground3Purpose3Uses and Limitations3Verification and Uncertainties4Getting Started5What is GNOME?5Setting Up GNOME5Requirements for Additional Functionality6Acquiring Data7Geographic Data7Wind Data8Current Data8Importing Data into GNOME9Universal Movers9Maps9Setting Model Parameters10Model Time10Spill Settings10Model Settings11Appendix I: Resources12GNOME Documentation12Current and Wind Data12

Background

Purpose

This guide is meant to supplement documentation that is already available for using GNOME. The basic concepts required to use GNOME, specifically for pumice rafts, are described in this methodology. However, any deviation from this methodology may require consultation with other documents. The GNOME team has published a Users Manual (2002), Technical Documentation (2012), and Data Formats document (2012). These and other helpful resources are listed in Appendix I.

On August 10, 2006, a pumice raft covering roughly 440 km2 formed as the submarine volcano Home Reef erupted for the first time since 1984. In the weeks that followed, the pumice raft traveled hundreds of miles westward, eventually reaching the Islands of Fiji and Vanuatu. Some pumice voyaged as far as Australia and Papua New Guinea by April 2007, but its greatest impacts were already felt. Ships that encountered the pumice between Tonga and Fiji were drastically slowed by the rafts. (Some sustained only minor paint abrasion, though others experienced clogging of seawater intake valves by pumice. Some crew members reported they were bombarded with flying pumice due to high winds.) In the hardest hit areas of Fiji, rivers and bays were completely covered for weeks to months. As a result, villagers were unable to fish or travel to their plantations. Pumice-filled bays also posed travel constraints, and many boats with outboard motors were destroyed or damaged by obstructed cooling systems. [footnoteRef:1] [1: Smithsonian Institute, Global Volcanism Program. (2006). Extensive pumice rafts between Tonga and Fiji during August-October. Bulletin of the Global Volcanism Network, 31(9), 2-5.]

From these experiences, the need to predict the movement of pumice rafts became apparent. While other methodologies exist to predict pumice rafts, the technical expertise and software required likely exceed that of many community planners. By utilizing the freely available General NOAA Operational Modeling Environment (GNOME) software along with other open-source solutions, a pragmatic and flexible methodology was formed.

Uses and Limitations

This methodology, like other published methodologies, produces a trajectory that is valuable insofar that it gives a general direction and timeline of a pumice raft event. In the case of the Home Reef eruption in 2006, the model predicted landfall on various Fijian Islands within days to weeks of actual landfall, a modest feat given over a month and 500 kilometers had elapsed. Had this methodology been available at the time, community leaders would have had certainty that at least some areas of Fiji would be impacted. In the same vein, modeling of the Havre Seamount eruption in 2012 correctly indicated the majority of pumice would travel eastward. Thus community leaders Background (contd)

would have been able to rule out any threat to Fiji, Vanuatu or other islands west of the International Date Line. This method is effective in gauging general risk from a pumice raft event, but meteorological forecast accuracy and resolution to date are not yet suitable for more localized and certain forecasts. It is certainly an improvement in warning lead time provided there is initial detection of the raft. This is especially true when contrasted by the Home Reef eruption, whose occurrence was not realized until pumice was encountered and traced back to the source. In such cases, GNOME can be run backwards, which can identify origin when coupled with satellite observations.When generating products from GNOME splots, pixels simulating pumice are outputted at very specific coordinates. This specificity should not be construed as certainty. Rather, red uncertainty particles (if minimum regret is used) should be treated as uncertainty bounds, and black forecast particles should be used as best track.

Verification and Uncertainties

While this methodology was tested with two historical events, it was not tested operationally, given no known pumice raft events occurred during this project. Historical, observed data was inputted into the model rather than uncertain, forecast data. For this reason, modeled historical events were initialized at only one point (the first point where pumice was observed by satellite). By comparison, an operational model would only be valid a few days out. Current and wind data used operationally for oil spills usually fail to produce trajectories within one mile of accuracy after 48 hours.[footnoteRef:2] Similar results are expected for pumice scenarios. As such, the model would need to be reinitialized as new forecast data was available and if possible, as new location data became available. Determining location could be accomplished using overflight data, satellite observations, and in situ observations. [2: Galt, J. A. (1998). Uncertainty Analysis Related to Oil Spill Modeling. Spill Sci. Technol., 4 (4), 231-238.]

In terms of meteorological data, further accuracy may be achieved by filling any gaps in satellite data. Gaps occur in filtered products because areas are automatically removed due to noise in the data. For the purposes of testing the model, filtered 1 ocean current data was used, even though 1/3 unfiltered data was available, and provided more coverage toward land. Even with observed data, some false-positives were generated in our modeling, and some actual pumice sightings were excluded. Ultimately the trajectorys accuracy is limited by the accuracy of forecast data utilized and variables which the model does not take into account (such as wave action). Getting Started

What is GNOME?

GNOME is a trajectory tool created by the United States National Oceanic and Atmospheric Administrations (NOAA) Office of Response and Restoration (OR&R). Launched in 1999, GNOME was originally designed for modeling the trajectory of oil spills. GNOME is an in-house model for OR&R, though it has been adopted by external response agencies for various operations, including tracking debris from the 2011 Tohoku tsunami. GNOME is supported for both Windows and Mac, and is freely available. The GNOME model has perfect algorithms limitations are only with accuracy of data that is inputted, such as wind and current data, and parameters such as windage (how much wind influences movement). Discussion of some of these parameters will follow, and additional resources are available here: http://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-tools/gnome.html

Setting Up GNOME

The GNOME software can be downloaded from the website above on the Download/Install page. The website has specific download and installation instructions, as well as a user manual. For general help with GNOME, you can consult official GNOME user thread available at https://list.woc.noaa.gov/pipermail/gnome-users/ The GNOME team there can help those with questions and may have additional resources and documentation available.Figure 1

This methodology only uses Diagnostic Mode, as Standard Mode is not designed for operational use. Switching GNOME to Diagnostic Mode is achieved by selecting Preferences under the File Menu, and then choosing Diagnostic as Model Mode (Figure 1).

Getting Started (contd)Requirements for Additional Functionality

ArcGIS OutputsSplot files, which represent spills, can be exported from GNOME for GIS software. GNOME saves these files as .ms* files, where * is a number between 3 and 7 (Figure 2).

Figure 2 Source: GNOME Users Manual

These files are MOSS files, an archaic ASCII file format. OR&R provides an extension that will import these files into ArcMap 9 or 10. You will need to install the GNOME Trajectory Import Tool from the Toolkit page:http://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-tools/gnome-toolkit.htmlFuture versions of GNOME are expected to allow exporting directly to shapefiles. Until then, anyone using open-source GIS software will need to use another extension or tool to interpret the ASCII file.

QuickTime Movie OutputModel runs can be viewed in GNOME, but they can also be saved as a movie. To save a model run as a QuickTime movie, the latest version of QuickTime is required.QuickTime can be downloaded for free here: www.apple.com/quicktime/download/

Acquiring Data

GNOME utilizes three types of data: geographic data, current data, and surface wind data. A wide range of sources, resolutions, and file formats exist for each type of data, but GNOME supports only certain types. This section discusses acquisition of data for operational and research use. If you are unsure where to obtain data, this section is meant for you.

If you already have data, the next section, Importing Data into GNOME, may be more pertinent, provided your data is in a format supported by GNOME. GNOME supports wind and current data that are ASCII or NetCDF and geographic data in .BNA (boundary atlas) format. Specifics of formats supported (such as grid types) are discussed in the GNOME Technical Documentation.DISCLAIMER: Data resources referenced below are provided as-is by their respective owners. Data availability and reliability cannot be guaranteed for operational use.Geographic Data

Geographic data can be acquired from the same source, whether research or operational use is desired. Geographic data is required so that GNOME knows when pumice reaches land so simulated particles do not jump land. The data also acts as a basemap within GNOME and when the Quicktime Movie output option is used.

GNOME requires .BNA files for this data. Using the GOODS (GNOME Online Oceanographic Data Server) website, these files can be generated based on user-specified coordinates and imported directly into GNOME. Go to GOODS: http://gnome.orr.noaa.gov/goods and use the Custom Map Generator under the Base Maps section (Figure 3).

Tip: The .BNA file is generated from Global Self-consistent, Hierarchical, High-resolution Geography (GSHHG) data. This high fidelity dataset can also be used in ArcGIS and other GIS software by downloading shapefiles from http://www.ngdc.noaa.gov/mgg/shorelines/gshhs.htmlFigure 3

Acquiring Data (contd)Wind DataGNOME uses wind data that contains both speed and vector. Most often, these data are represented as u and v variables (zonal and meridional respectively). The datasets available for wind vary, especially for operational use. For global scales, the Global Forecast System (GFS) model output is readily available in NetCDF 1 and 1/2 resolution on the GOODS website (see GFS under the Winds section). For United States use, the NAM model and buoy data are also available on the GOODS site. If those models do not meet user needs, other models could potentially be converted to NetCDFs (e.g., from grib2 to netcdf).Historical wind data can be accessed through a number of sources as well. One example is the National Climatic Data Centers Blended Sea Winds website, which provides 0.25 resolution data in NetCDF format.*

*In 2011, the AMSR-E instrumentation on the Aqua Satellite failed. As a result, data from the NCDC after September 2011 is experimental as of the writing of this guide.

The NCDC data is available at http://www.ncdc.noaa.gov/oa/rsad/air-sea/seawinds.html#data. There are numerous download options, including FTP and OPeNDAP. OPeNDAP should allow merging of multiple timesteps ( 6hrly, daily or monthly) into one file. If, however, you need to merge multiple files, or if one file is too big, see the GNOME Technical Documentation (Section 1.2.2.4 Data in Multiple NetCDF Files).

Current DataLike wind data, operational current forecasts are available from a variety of models depending on the region. The GOODS website provides 1/12 resolution in NetCDF format through the Hybrid Coordinate Ocean Model (HYCOM), and RTOFS. RTOFS is provided in 2-day nowcast or 6-day forecast and HYCOM is provided with 5-day forecast. Current data for historical use can be obtained at 1/3 and 1 resolution from NOAA Ocean Surface Current Analyses Real time (OSCAR) data here: http://www.oscar.noaa.gov/datadisplay/The OSCAR data is particularly seamless to use, as the website can automatically create NetCDFs with 5-day resolution data over a user-specified period. Alternatively, monthly means and long term means can also be generated. Note that while 1/3 data is available, it has not been filtered. For quality control purposes, 1 data may be preferable. Importing Data into GNOME

Setting up GNOME can be easily accomplished when inputs and settings are filled in the right order. For example, trying to create a spill will yield an error if a map has not been loaded yet. This section discusses how to input basic data first, so you can then begin inputting other parameters. More advanced parameters are discussed in the next section.GNOME is broken up into four submenus: model settings, universal movers, maps, and spills. When GNOME is first opened, there will be nothing under Spills, Maps, and Universal Movers until objects are added. Once you begin loading objects and settings into the GNOME environment, you will want to initially save your project by going to File Save Diagnostic File Save (.SAV).Universal MoversA universal mover is any forcing that influences the movement of modeled particles. This includes winds, currents, and eddy diffusion. To add a universal mover, double click on Universal Mover, select either Currents or Winds-Variable. Then click load (Figure 2). Browse to the location of the file. (Remember only NetCDF and ASCII files are supported)After selecting the file, two dialogue boxes will appear. The first will ask if you want to reset the model start to the first time in the file. Model start time can be changed at any time, but if you want to start modeling at the first timestep in the data, select Yes. You will also be asked if you want to shift the latitudes 360. Lastly, you will be asked to input the uncertainty of the information. This includes at what point the data becomes uncertain and its degree of uncertainty. The GNOME technical guide suggests 3 hours for wind and 48 hours for currents, based on experience (Section 15.1.1).MapsTo load a basemap into GNOME, simply double click on Maps in the side menu and browse to the location of the .BNA file.Refloat half-life This setting indicates whether the substance is subject to rewashing into the ocean upon landfall, and if so, how soon it would refloat.

Setting Model Parameters

Model TimeSome of the most important parameters in GNOME are times. If times do not line up, the model simply will not run. There are three types of times to take into consideration: spill release time, model period time, and data time. Spill time is chosen when creating a spill (discussed next). Model period time is edited by changing start time under model settings. Lastly, data time is within the NetCDF or ASCII data. The data can extend beyond the modeled time, but the modeled time cannot extend any further than the end of the available data. The spill release time can start at or after the model start time, but the spill release can never be before the model spill time.Spill SettingsTo create a spill simulating pumice, double click on Spills. Change the following settings accordingly:Type - There are four possible spill types, three of which may be useful. Point/Line Source Splots Creates a spill at a given point of longitude and latitude. Particularly useful for fast modeling or if only the location of the pumice-producing volcano is known Sprayed Dots May be useful if the shape and volume of the pumice raft is known. However, the resulting trajectory may differ only marginally. Splots from GNOME Splots File Allows user to import splots saved from a point in time (splots can be saved by going to File Save GNOME Splot Files for GNOME Analyst). This is useful to run multiple scenarios with the same spill. This is also an alternative work-around for once GNOMEs input file size limit is reached.Pollutant Pollutant type should be set to non-weathering, as pumice does not undergo the same diffusion, evaporative and other processes that oil goes through.# Splots The number of splots (spill dots) should be set to at least 1000. Lower than 1000 may cause statistics to suffer. Amount Released The released amount can be estimated by overflight data and inputted in meters cubed. Alternatively, average pumice raft size can be inputted.Windage/Persistence These settings are slightly hidden, but are very important. Within the Spill Information dialogue box (accessed by double clicking Spills) click Windage. Windage represents how much an object protrudes from the surface and is influenced by wind motion. 1-4% (the default) is valid for pumice. Persistence represents how (if at all) the object sinks and resurfaces due to buoyancy. This should be set to infinite.Setting Model Parameters (contd)

Model SettingsModel Run Duration: How far out the model will run from the start pointMinimum Regret solution: When checked, uncertainty particles represented as red dots will be included in the model.Show Currents: If selected, current vectors will be shown when the model runs. Selecting this may reduce performance. This can also be chosen for wind vectors (see Universal Movers Wind File Show Velocities checkbox).Computational Time Step: For all intents and purposes, this should be set to the lowest interval at which your data is available. If you have 6-hourly wind data but only daily current data, the interval should still be the lower of the two. Emphasis is put on computational interval, for output timestep and the timestep used to compute that output are two very different things. Suppose you have 6-hourly data and are computing it at a daily interval, with the start time at 0z. The resulting computation would not factor in data from the 6z, 12z and 18z frames, effectively lowering temporal resolution, and thus accuracy. If you wanted to accomplish an output that was 1 timestep each day, you could do so upon export. When saving as a splot series or QuickTime movie, you will be prompted to input time interval.

Appendix I: Resources

GNOME DocumentationGNOME Websitehttp://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-tools/gnome.html

Users Manualhttp://response.restoration.noaa.gov/sites/default/files/GNOME_Manual.pdf

Technical Documentationhttp://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-tools/downloading-installing-and-running-gnome.html

User Threadhttps://list.woc.noaa.gov/pipermail/gnome-users/

GNOME Toolkithttp://response.restoration.noaa.gov/oil-and-chemical-spills/oil-spills/response-tools/gnome-toolkit.html

Current and Wind DataPO.DAAChttp://podaac.jpl.nasa.gov/

GOODShttp://gnome.orr.noaa.gov/goods

NCDChttp://www.ncdc.noaa.gov/oa/rsad/air-sea/seawinds.html

OSCARhttp://www.oscar.noaa.gov/

HYCOMhttp://hycom.org/

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