2008 - June - 20th

Yesterday, I had the opportunity to attend a field tour of the Angora Fire hosted by the Fire Safe Council of Nevada County and the Sacramento-Tahoe Society of American Foresters Chapter. The tour was attended primarily by agency folks, retired US Forest Service and CalFire Foresters as well as the occasional private citizen (a.k.a., me).

The Angora Fire started on Sunday June 24th, 2007 by an illegal campfire near Seneca Pond. In less than 2 days, over 250 structures on private property were destroyed. It was one of the largest fires on recent record for the Lake Tahoe Basin. The fire consumed most of it’s 3,072 acres during the first three hours when weather conditions were at their most extreme. On that day, conditions were ripe for a fast moving fire and someone left their campfire unattended, perfect recipe for a fire storm. Firefighters reported seeing 200 to 300ft flames.

Those are the facts of the fire. However, the tour didn’t focus on the fire, but rather, what activities before, during and after the fire that helped to mitigate some of the effects of such a devastating fire.

Our first stop was at the end of a small street called Shoshone St just off of N Upper Truckee Rd just west of South Lake Tahoe.

North of this location, houses were destroyed. However, south of this location, homes survived primarily because of a 200ft reduced fuel break that had recently been completed along the community. This fuel break had astounding results. Though the fire burned hot here, it was, after all, a very hot day, with fuel moisture at an all time low and winds gusting to 50mph, the fuel break kept the fire on the ground rather than in the tree tops and many homes were spared the inferno that was created to the north. It also created a safety zone that allowed firefighters to do their job, protect valuable resources – homes.

Looking north from end of Shoshone St at newly constructed homes and severely burned hillside in background.

One year after the fire, within the fuel break area, we find plants such as lupine, mule ears, manzanita and mountain whitethorn starting to re-populate the understory. In stark contrast to areas that were severely burned where no understory growth is occurring.

Our second stop was just behind the South Tahoe High School off of Lake Tahoe Blvd. At this location, in a successful attempt to save the High School buildings as well as a government center and critical infrastructure, USFS fire personnel decided to light a backfire. Again, the fire burn severely, but moved away from the school rather than towards it and saved the school from damage.

We didn’t have time for another stop but USFS personnel discussed rehabilitation of the dozer lines created during the fire and the removal of noxious weeds – always a concern after a severe fire. We also heard about their ground and aerial application of mulch and their efforts to remove hazard trees and to reforest/revegetate the most severely damaged areas.

One revealing fact that was repeated often was that in a wind-driven fire, spot fires started from flying embers is a known hazard. Given the location of the fire, the embers from the wildland fire easily ignited homes adjacent to the forest. It was then embers from the house fires that ignited even more homes further into the subdivision.

Two years after the fire, northern California finds it self at nearly the same conditions as that June day in 2007. Conditions are warm and dry, coupled with current low fuel moisture content and another fire like the Angora Fire can occur on our next windy day. Please be fire safe! That means maintain your defensible space, consider changes in your home siding and roofing to less flammable material and don’t leave a camp fire unattended! Please visit the Fire Safe Council website or the Fire Safe Council of Nevada County for more information on how to be better prepared for a fire.

A full report of the Angora Fire can be found here: An Assessment of Fuel Treatment Effects on Fire Behavior, Suppression Effectiveness, and Structure Ignition on the Angora Fire

2008 - June - 10th

It's been a while...

Where did six months of my life go?

Sorry I haven't kept up with this blog as much as I had hoped. But I'm back and I have a new hard copy map for purchase on my Tools & Maps page. Please check it out!

I hope to have several more maps ready for purchase by the end of the year, just in time for the holidays and gift giving. If you know someone interested in the Truckee-Lake Tahoe area and can't think what you should get them, please consider my maps.

I'm not going to promise that I will update this blog anytime soon, as I haven't! But please check back as I hope to have a couple of tutorials on Google Maps ready for printing in the next few months.

2007 - December - 26th

Happy Holidays!

Happy Holidays Everyone! I hope that your holiday season is going well.

Not much new to write about today. I did pick up some new code for some weather forecast stickers. You can click on them to get Truckee's weather forecast!

I am also getting my website re-designed! The functional layout and look should be improved upon. In addition, I will be coming out with some cool printed maps that you can purchase. They will be primarily centered around the Truckee/North Tahoe area but I do plan to do some other locations (like New Zealand). Hope you all have a great New Year!!

2007 - November - 3rd

Aerial Photography

I often get requests for aerial photographs. Where can I get the latest aerial photos for free? How can I get the same image as the ones that Google uses? Why are Google's images so old?

Aerial photography is a standardized industry and taking those photos (either by satellite or air plane) takes time and money. There are literally thousands of companies that capture images of our earth from a remote location. Aerial photos, satellite images and other such products are the result of what the industry calls remote sensing.

Remote sensing is the act of collecting information from an object while not being in direct physical contact with that object. Remote sensors (the equipment gathering the information from the remote object) are varied and complicated. Different sensors can gather different wave lengths of the electromagnetic spectrum so that you end up with very different image products, so that in turn can be used in a variety of applications. For example, near infrared images are often used to classify on image into vegetation types because the of the nature of how light passes through and is reflected by vegetation is its various stages. You can read more on the topic at the NASA Remote Sensing Tutorial page. You can read to your hearts content about TM Imagery, SPOT and plain old aerial photography.

However, most folks just want a natural color image for a map base. Depending on the final application, resolution, date and quality of the image (no haze or smoke) are the most important features folks are interested in.

Resolution

The resolution of aerial photos (or satellite imagery) is really dependent on one main factor during which the images were taken: Height (or distance) the remote sensor is from the surface of the earth. Regardless of how the final product is eventually sized with enlargement or reduction (or zooming in or out), the original scale at which the photo was taken will determine what sort of features you will be able to distinguish (i.e., large rivers vs small streams). So, when shopping around for aerial photos, find out what the original resolution or scale of the aerial photo is. For example, if you are hoping to distinguish individual homes and trees in your neighborhood, you will most likely need an image with a pixel resolution of under 1 meter (or a scale of 1:10,000 or greater).

Date

This is an obvious one, when was the photo taken? Are you looking to compare different years, highlight development or a change in vegetation?

Quality of Image

The quality of an image depends on the type of remote sensor used and weather conditions. Unless you really know what you are looking for, you don't have much control of the type of sensor used, however, you can look for images that were taken in summer. Why summer? In North American, the clearest days often occur during the summer months. There are exceptions, of course, however, you will be hard pressed to find any aerial photography taken during other times of the year unless they were taken for a specific reason. Prior to purchasing any aerial photography, ask if the images are haze and smoke free

So what about free photos and the ones that Google uses?

The USGS has a library of Digital Orthophoto Quadrangles (DOQ). These can be accessed from a variety of places and are entirely free! We pay our taxes from some reason right? Well, here's one of 'em. They usually come in TIFF format, are geo-referenced, and are usually about 1m in resolution. However, they are black/white photos. In addition, they are not often updated. Another government source (read - free) are the images from the National Agriculture Imagery Program (NAIP). The resolution on these are at 1m as well but they are natural color (with some available in near IR for some areas). These are also available from a variety of sources. Another issue with these as they for taken for agricultural purposes, they do not cover cities or urban areas.

As far as the images that Google uses, have you noticed on the right hand, bottom side of the image there is usually a reference to the image originator, like DigitalGlobe, Sanborn or TerraMetrics. These guys want money for those images! And Google, being inexhaustibly rich, can pay for an entire world's worth of images. Keep in mind, however, that these images are not real-time (imagine the cost!) but they are usually the best (clearest and latest) available for a given area from their image sources. There are, of course, other image sources. There are thousands of local aerial image providers throughout the country and I am sure there is one near or in your town! You can look them up in your phone book under Aerial Photography, Photographers Aerial or Surveyors Aerial. Here in Truckee, CA, we have GeoCADD. I'm sure there are others but that is who I use. In addition, there are online sources like Topozone, Terraserver and GlobeXplorer.

Hope this was useful!

2007 - October - 23rd

This is my first ever blog and my first ever blog entry.

When deciding to put together a quasi-blog space on my website, my first thought was "what would I write about?" After further thought, I figured that this space could be used to impart some tidbits of information that might make your life easier while navigating our geospatial world. I will also write about some of the projects I am working on. Hopefully, the solutions I find for one client can help another or even you!

So, this isn't really a blog - you can't respond to my entries here on this website, but you can email me and I will respond directly to you as well as put your comment/question on this page for others to benefit from.

I will try to post an entry at least once a week. Topics will most likely revolve around GIS and Geography, however, since my interests are far flung, so to may this blog fling.

Just what are projections and why doesn't my data match up?

When I first started out working as a GIS Consultant, many folks were still using software programs that did not "project on the fly" (i.e., ArcView 3.x). With ESRI's ArcMap and AutoDesk's Map 3D, problems with projections are usually hidden and the casual GIS user need not worry about projections. However, every now and then, they rear their awful heads and some one has to deal with it. If you don't have someone like me around to help you out, they can be a pain. Here are a few pointers to help you figure out what a projection is and why you need to know a little bit about them.

So I'm asking you again, just what is a projection?
A projection is just a way of representing a curved surface (the earth) onto a flat surface (a piece of paper or your computer screen). This site (yes, it's a Wiki page) offers a more complete definition along with lots of diagrams and explanations for a few of the projections that are out there. One thing to understand about projections is that since the earth is a sphere (and not a perfect sphere), a certain amount of distortion will occur when you try to represent the earth's surface on a flat piece of paper. To add insult to injury, depending on where you start your coordinate system, the farther you get from your origins, the greater the distortion. So many map makers from around the world, ever since people started putting pencil to paper to try to map our surroundings, have created customized projections to minimize both distortion and scale errors. So one projection that was developed to best represent, say, Antarctica, will not be very useful to represent the Fiji Islands.

The projections most often used in the United States vary from location to location. In addition, if you obtain your data from an agency source, that agency may have a policy to use a certain projection for all their datasets, whether it's appropriate or not. The following list of projections is what I have found for most GIS layers here in the United States:

Country-wide Datasets
Geographic Coordinate System
Lambert Conformal Conic

State-wide Datasets
California - Albers
The great State of California developed their own! It's a modified Albers projection. They just had to be different...
Nevada - UTM Zone 11
Most data layers I have gathered for the great State of Nevada has been in this projection. All federal agencies seem to be on the same page.

County-wide Datasets
Generally, as counties are small and often have to deal with very small parcels of land, they are especially interested in accuracy within their area. Just about every county dataset I have used is in State Plane Coordinates.

Federal Agencies
Many federal agencies seem to stick to UTM (Universal Transverse Mercator) or the Geographic Coordinate System.

Now, you many be thinking, that it's? No, that's not it. There are many more projections out there. In addition, there are things called "datums". No, that the singular of data (though that is grammatically correct), but "a reference from which measurements are made". A projection could be based on a number of different datums (in North America you will most often see NAD27, NAD83, or WGS84). There are also different zones for different geographic regions for the UTM coordinate system as well as the State Plane coordinate system.

So now do you see why your data doesn't match up? If course, if you are using a newer GIS software package you probably do not have the problem of your data not matching up. As long as the GIS Specialist who created or maintains the data you received did their job and correctly defined the projection for your data layer, the software does the complicated math for you on the fly and ensures that your data "lines up". If you want to know more about projections, datums and much more you can visit the links scattered above or you can just ask me. If you found this useful, please let me know!