Using GIS to find meteorites

When a meteorite fall occurs, meteorite hunters often just grab a map, a GPS, and head for the fall. While this works, there is a better way to plan an expedition using GIS (Geographic Information System) software.

Using open source software, free data from the government available online, and a few hours these meteorite hunters will know a great deal more before they even get to the meteorite fall. This, in turn, will increase the number of meteorite fragments recovered and lower the cost in terms of money, time, and effort expended.

GIS is software that takes information with a geographic component and displays it on a map. Like lines showing where rivers and creeks are, or dots displaying individual cases of west Nile virus. Each line or dot of data can be queried to tell you more about the data record, like the name, flow rate, and depth of a river or the name, hospital, age, etc of a West Nile virus patient. Essentially a database with georeferencing. Each database of information is called a layer. You can easily obtain layers for free of hydrology, cropland use, rainfall measurements, soil type, surface ownership parcels, and many cultural datasets. Each and every layer will be stacked on top of the basemap layer to give a representation of the land. Any particular layer can be made invisible or translucent to have other layers more apparent.

There are a variety of GIS programs available, the most common one is ESRI’s ArcView but it is $1,600 per seat and overkill for the needs of the meteoriticist. A better solution is the open source programs like Quantum GIS or gvSIG. Both are free, full fledged GIS programs and can do spatial analysis. At this time, Quantum GIS is recommended, as it is free, easy to learn, intuitive to use, and fast to render datasets even on older laptops. Download a copy at Qgis.org. All GIS programs will benefit from a good video card and more RAM. A little GIS training would be useful as well.

Google Earth is a low grade non-GIS mapping tool. It does let you put point layers down, but the free version won’t read other data layers or do any spatial analysis. Also, it won’t let you print out large maps. This is a big drawback. Ironically, non GIS users think it is great, but it is a toy compared to real GIS programs.

The immediate GIS needs of the meteorite hunter will boil down to two critical questions:
a) Where is the strewnfield? and
b) What is the strewnfield like?

To meet these needs there are some data layers that need to be obtained. The first will be the basemap layer. A basemap is the important reference layer that all other layers are laid down upon. For a Texas project, the basemap would be the outline of the state of Texas, or satellite imagery, or the complete topographic map of the state of Texas. Whatever basemap makes sense to you is the right one. Given that the average meteorite fall should be less than an area of 30 km x 30 km, I recommend using a topographic map as the basemap.

Now that a basemap is chosen, we need some more data layers to help with the hunt:
-Major Roads
-Minor Roads
-Private Roads
-Railroads
-All hydrology, lakes, rivers, creeks, etc
-Cropland designations
-Satellite photos (you want to spot buildings for reference)
-Vegitation designations
-Cadastral data (Surface Ownership polygons containing owner names)
-Soil type
-Topography

Most of these should be available online from some government agency for free or for a reasonable charge. A few may not be, but as long as you have most, you are ahead of the game. Each layer has a use to the meteorite hunter, and each use I will outline here. Also, it would help to take an online GIS class.

Roads, major, minor, and private along with railroads are important on three levels. First, if the fall was in a remote area this layer will tell you how close you can get to the target by wheeled vehicle. Second, this layer may be more up to date that the maps you have available so you may discover you can drive into the target when 10 year old published maps say you have to hike the last 5 km. Third, in the US and some countries, meteorites found on public roads and their right of ways are fair game for anyone. Private roads will require permission to hunt but it is good to know which is which.

Hydrology becomes important on remote locations. It may be useful to know the names of streams and reference field notes with hydrological features. For old falls, like the Deport iron meteorites, I discovered that within 20 meters of creeks the irons were buried deeper due to presumably flood sediment. In the case of Ash Creek fall in the town of West, Texas, the hydrology simply helped define borders and property boundaries that were not seen on published maps.

Cropland data is great to have to know where to start the hunt as soon as you arrive on location. Before you leave you can know that in April, the north half the strewnfield should be fields of corn. It could be that there are fallow areas to the south. Once the meteorite hunter arrives on the scene, confirmation of cropland data will be needed. In the case of old finds, meteorite hunters could focus on talking to farms of specific type, like Cotton which tends to be soil that is more disturbed than other crops. I’ve used this in my Niningeresque canvassing of some areas in West Texas to recover several meteorites.

Satellite photos are great in many ways. First, it gives you the size of a parcel of land based on ground cover color. In the US, a ‘section’ of land is 1 square mile which is 640 acres. A aerial photo may show 5 parcels in that section which hints that you may only have to get permission from 5 people in order to hunt. The photos also show areas that are timbered or have other vegetative hints which indicate good or bad hunting areas.

Vegetation designation is different than cropland as this should cover all the area and not just agricultural areas. It could tell you that the vast majority of the ground is covered in 2 centimeters of moss which is terrible. Like it was for us hunting an old fall in Stelldaellen, Sweden but great for a new fall. In advance, poor hunting areas can be identified such as swamp and marsh areas, which will improve the hunt by not wasting time in these poor areas and shift the effort of the hunt to areas indicated to be higher ground with sparse vegetation.

Surface owner parcels is the same as real estate parcels. Basically, it is polygons of owners land shapes. This may be a hard layer to obtain but it is quite useful. You will know who owns the land, and can make phone calls without having to knock on a tenant or renters door and get the name of the owner. This layer will save the meteorite hunter large amounts of fact finding time in the field. Remember, the owner can give you permission to hunt the land and keep the meteorites found, not the tenant.

Soil type layers are useful more with old falls and hunts after older finds. Had this layer been available to me on an expedition to Karatu, Tanzania, I would have aborted that target. This is because when I got to the Karatu fall area, I discovered that the area was volcanic with black rocks with a ferrous component and I was looking for stones from a 40 year old fall. It was terrible ground to try to hunt, and near impossible to train the locals to distinguish meteorite from meteorwrong. Most US states have good soil type maps.

Once the meteorite hunter is on site, there are two layers that will need to be created. First, is a point layer that will be locations of all the meteorite finds. This will be needed to begin seeing trends and establishing a strewnfield direction line. The second layer will be a polygon layer which will show the areas which have been searched and reduce duplication of effort. With this layer, it will become useful to the meteorite hunter to use visible landmarks that can be seen from the topo layer or the aerial photography to start and stop his search areas. In the case of the Deport iron hunt, I used telephone poles and the edges of farm fields as my landmarks because they showed up on 1m resolution aerial photos.

These layers can be obtained from many sources. I’ve discovered that the source for the best and most accurate data to be at the lowest level of government. In the case of the Ash Creek, Texas the 1m resolution satellite imagery came from the TNRIS (Texas Natural Resource Information System), the topology from a CD product I owned, and the land cover came from another state agency. Of course, I had to ask local meteorite hunters where they had found stones and their size. This then gave me the most definitive map on the Ash Creek fall known to exist. I went on to find 8 stones coming in at half a kilo.

In summary, GIS should be in every meteorite hunters toolbox along with his magnet, cane, hat, Doppler Radar, water bottles and hiking boots. It is the tool that will presort good from bad terrain to optimize the little time you have at a fall. On site, it can be used to better track known finds to flush out the strewnfield. Further, it should be used to quickly and effectively identify surface owners to contact for permissions. To learn more about it, you can go to www.learninggis.com, or take one of their online GIS classes.

Good luck, and good hunting!

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