Where Am I at?

What a common question.  It has been my fortune many times in my life to not know where I am at.  With the advent of GPS, we are able to instantly know our exact location within plus or minus a certain parameter, but always close enough to get us to our destination.  As the technology improves, the factor of error becomes smaller.  In this beautiful age of gadgetry, we often rely on batteries to make the tools work.  This can be a very unfortunate issue if that is all we know how to do.  While I was in the military, we would often teach other soldiers how to use known landmarks, or their known position to help them find themselves.  This awesome method is known as triangulation.

Through triangulation, you are able to figure out based on the information available to you, where you are.  In the first example, you decide to drive some forest service roads.  You know that you just came from point "X" and you haven't been paying attention for a while.  After making a series of turns, you finally decide that you are lost.  Lucky for you, you know where you came from,

In a much simpler example, you are in a city.  In many US cities, the streets are at times laid in a grid and are labeled which direction they go.  If this is not the case, then it still doesn't matter.  Just by looking at your map, you can orient yourself based solely on the direction that you are walking.  This in itself, is a very basic form of triangulation.

Limitations in Satellite and Aerial Imagery Collection and Production

Introduction

It is inevitable that everyone has something to hide.  This includes even the most honest of people.  Whether it is that they cheated on their diet, to the candy bar that they stole when they were six, people have secrets that they either need or want to keep.  The rationale for keeping secrets isn’t always so clear or even logical.  Some of these secrets are exposed by taking the higher ground.  By taking the higher ground and using some form of aerial imagery, it is possible to expose some of these secrets, whether dirty or innocent.  In the case of the moonshine distiller or the marijuana grower, the reason to hide this secret is easy; getting caught is bad and cuts into their profit margin.  In the case of a state or government, the reasons may not always be so clear.  Generally the reasons usually have to do with national security, and the general welfare of the people in the care of the state.  However, the successful grower or distiller will find or create methods to conceal their labors, through methods of camouflage, misdirection and other creatively available methods.  Governments, in an attempt to conceal sensitive information, will also do the same.  It is herein that the question lies: what am really I looking at?

“Ground Truthing”

The easiest way to confirm an aerial photo is to physically visit the location, if at all possible.  This method of verification is loosely termed ground truthing. Ground truthing carries a couple of definitions.  However the basic idea of ground truthing is to verify an image is accurate in its depiction of the terrain and to verify that no anomalies have occurred.  In an extreme sense, ground truthing can also be used by strategic planners to ensure that a military asset is what it is meant to be.  An easy but good example of this occurred during World War II and the ensuing years after the war.  In order to trick the enemy, the allies would place dummy tanks complete with dummy tank tracks to fool the photo interpreter (see fig. 1).  

Fig. 1

The tools often used for this type of campaign generally relied upon deception, misdirection and camouflage.  In a non-military environment, a good reason to ground truth an image is that an image may contain some unknown variable.  However, without visiting the site, the image interpreter may be unable to accurately discern certain features such as a house that may be hidden within a grove of trees.  In ground truthing, there also may be errors in the imagery.  Some of these errors can be classified as errors of omission or commission.  An error of omission may occur when an object is not classified, even though there is a classification for that object.  For instance, though a manhole may be visible on an aerial, the interpreter of the aerial image may fail to classify it as a manhole.  An error of commission may occur when an object becomes classified as another object that it is really not.  An example of this would be an asphalt road labeled as a train track. (Wikipedia; Ground Truth).  It is important to ground truth because remote imagery has many limitations.

Limitations in Collection and Production

In aerial mapping and remote sensing, there are many limitations which can affect the final outcome of the product.  Some of these limitations are directly related to the sensor, the airborne platform, the environment, the interpreter/user of the information, and multiple other factors such as cost.  In order to mitigate these effects, there are a variety of solutions which may be employed. 

The biggest cause for error is human.  Being human is in itself a limitation that enables us to do or not do certain tasks well.  It is for this reason that one of the limitations if imagery is human error.  In classifying objects in an image, the image is only as good as the interpreter.  As discussed previously, this is one of many reasons why we ground truth.  Although we are human and this is a limitation in itself, we are also limited by how well we understand the technology, our ability to exploit the technology, and the ability of the technology to adequately perform the required task.

One of the most obvious limitations in acquiring imagery is the weather.  Weather factors such as cloud cover, fog or snow may make it difficult to obtain quality images for both satellites and aerial platforms.  Additionally, weather factors such as wind may make it difficult for an aircraft to fly within tolerance of the planned flight path required to obtain quality data.  Even though weather has its limiting factors, there are ways to overcome this.  Sensors attached to a space based platform are rarely affected by weather. Radar sensors such as Synthetic Aperture Radar (SAR) and side looking airborne radar (SLAR) have the ability to penetrate clouds.   In general, space based platforms are able to outperform the aerial platform as the space platform is not weather dependant.

Trees and other ground features may also create limitations in obtaining quality imagery data.  Trees and shadows from trees and other objects may make it difficult to see objects on the ground.  As discussed previously, radar sensors have the ability to penetrate clouds.  Unfortunately, radar sensors consistently fail to penetrate through dense objects such as forests.  This makes it difficult to acquire good data about ground topography and ground features from radar in forested areas.   The best way to verify objects on the ground is through ground truthing and supplementary ground survey.

When acquiring aerial imagery, the cost and time of travel must also be taken into account.  It is possible for some companies to affix multiple sensors at one time.  As technology becomes better, some sensors have incorporated multiple modes of acquisition.  An example of this would be an operator such as Keystone aerial surveys out of North Philadelphia (KPNE) who use the UltracamX.  “The UltraCamX is a multispectral imaging sensor capable of capturing panchromatic, red, green, blue, and near infrared data simultaneously” by incorporating multiple sensors, the operator has the ability to better serve the client through faster turnaround times. 

Another consideration is the need to set up control points on the ground for aerial surveying.  These control points on the ground provide a way to correlate the images collected with the ground grid coordinates and elevations.  Setting up control points is also a form of ground truthing.  Setting up ground control points is a project cost and requires additional time and coordination.  It requires a survey crew to go out and set up panels, and survey the panels location.  A process known as analytical triangulation is used to correlate the ground control points with the aerial data.  In the article titled “From the Ground Up: Direct Georeferencing in Aerial Photography” by Mark E. Meade, the author states that one way to overcome the need to set up control points is to use Airborne Global Positioning Systems (ABGPS).    By using ABGPS, it is possible to know the aircrafts position relative to the earth at all times.  With the advent of Airborne Global Positioning Systems (ABGPS), the number of control points required for a project is greatly reduced, thus saving time and money.

There are different advantages and disadvantages to the use of satellites versus an aerial platform.  Satellites are generally more able to acquire large areas with relative ease, whereas an airplane may require several flight lines and multiple control points in which to gather the information.  Aerial platform radar systems tend to be a good method to map an area quickly and efficiently with a relatively lower cost, because the flight line tends to be wider and would require fewer flight lines flown In this same way that radars are used on aircraft, this is a sensor that also translates to a space-borne platform. 

A satellite can often produce the same image that an aerial mission would acquire, but would be at a greater cost.  For small projects, satellite may not be cost competitive with the aerial platform.  For large projects, the time saving benefits of using satellite might outweigh the additional cost.

Let’s just propose an example.  In this example I need to do a noise abatement study because commercial traffic at Prescott Love Field (KPRC) in the last two years has increased by 15%.  The surrounding neighbors keep calling the City of Prescott airport manager and complaining about how noisy traffic at the airport has become and how they can no longer sleep at night.  It is bad business to drive this traffic away, since this is the very traffic that is bringing money in for the city.  In an effort to solve this problem, the city manager along with various other authorities would have to come up with a way to move the traffic away from the housing development.  This would keep the airport manager employed and the neighbors happy.  In order to effectuate this plan however, an aerial image of some sort must be acquired in order to show any new development that may have taken place.  The City must minimize the cost required to perform this study. 

Aerial imagery of this nature is readily available through various vendors.  One of the more prominent online vendors, mapmart of mapmart.com prices imagery with a two foot resolution for satellite at $822.  This same area can be acquired for $567 if you desire imagery from an airborne flight.  Although this is a savings of $255 (even for large companies that is a decent savings), the imagery is slightly outdated (See Fig. 4 below).

Fig. 4

It would likely cost even more money to have aerial photographs of this area taken specifically for this project.  The problem is that the City must balance the cost of the data they need against the quality of the data.  If the Airport Manager believes that growth to the area surrounding the airport has been minimal over the few years, the older data may be acceptable.  If the Airport Manager is unsure of how much growth has occurred recently, or if recent growth has been substantial, the manager may choose to have aerial imagery collected specifically for this project, despite the increased cost.

Conclusion

Though there are limitations to all forms of imagery data collection, satellites generally seem to have fewer limitations.  There are still applications in which data from an aerial platform may be preferable to data from a satellite.  Because both forms of imagery are imperfect, the only way to know for sure what is being seen is to ground truth the data.  Through real time verification, we can ascertain the properties of hidden marijuana plants or mislabeled tanks with the all inclusive fake tank tracks.


For a complete works cited please leave a comment.

Where Have They Been?

One of my interests is looking up N-numbers on the Federal Aviation Administration's (FAA) website.  I don't always know why I find this interesting but, once in a while when I see an airplane that has something unusual attached to it or an aircraft that I may not recognize, I save the N-number and look it up at http://registry.faa.gov/aircraftinquiry/NNum_Inquiry.aspx.  Sometimes, I look up aircraft and what they have been up to  by going to Flightaware.com and looking up their N-number or in the case of Keystone Aerial Surveys Inc. you can even search it by their ICAO callsign; thier callsign is Footprint (FTP).

Out of all the survey aircraft that I have looked up, I find that most of these are usually of the Cessna or Piper variety.  Occasionally I find that there are a few aircraft as in the case of Fugro Earth Data and Aerial Viewpoint, that use other various airplanes.  Generally, the aerial platform used tends to be a high wing single engine piston  aircraft or a light twin.  The one exception happens to be the Rockwell Aero Commander, which is a high wing piston twin.  High wing aircraft offer stability and a downward looking view. 

All of this may seem nosy, but one aspect that is made readily visible is who and what kinds of persons are hiring aerial survey firms.  I think of this as being competitive by using all available public knowledge to my benefit.

A Brief History of Aerial Cameras and Remote Sensing Technologies

Introduction

There are many ways to extract desired pieces of information about the earth's surface.  The method is generally dependent upon the tools available to the practitioner.  Without the necessary tools, the quality of information available to the practitioner is severely degraded.  This accuracy of the information is reliant upon the methods used to collect the data, and the reliable interpretation of this data along with other variable factors. As it is in many information gathering occupations, this same reasoning is applicable to aerial survey and remote sensing techniques.  From the early beginnings of balloon photography to the prolific use of aerial photography in World War II (WW II), the basic tool was the camera.  As the technology progressed, it evolved into even more advanced methods of gathering information.  These methods consist mostly of the aerial camera and satellites.  The way in which their evolution occurred, although similar, is decidedly different.

Development of the Aerial Camera and Remote Sensing

One of the earliest uses of the camera as an aerial tool was reconnaissance in WW I.  The camera as a tool of war gave observers a more accurate way to record the enemy’s positions and activities.  Originally, the cameras used for aerial surveillance were no different than cameras used in everyday life.  It was in World War I that cameras used for aerial survey applications became more sophisticated.  People began experimenting with different parts of the light spectrum to create better imagery.  Some of the advances and experiments during this era included layering different colored films to get different results, a three lens multispectral camera, camera stabilization and stereo-photos.
It wouldn’t be until after the war that a good camera for aerial survey would be created.  This advancement was due to an invention by Sherman Fairchild.  “Fairchild’s invention was to create a camera shutter sandwiched between lenses, thereby reducing the significant image distortion previously hampering aerial photography and mapping” (Sherman Fairchild: Totally Explained).  Fairchild sold his invention to the military and lost money on the deal.  Although he lost money, Fairchild would make other advances in aerial survey.  He eventually started Fairchild Aviation, and worked to create a better aerial survey platform.

Between the World Wars, aerial survey had to find a niche to remain viable.  In the United States, there were lots of farms and most farmers had no idea how much land they really had and what was useable.  Part of the Farm Credit Act of 1939 allotted for aerial mapping of these farms.  In fact the largest user of aerial mapping during this time period happened to be the U.S. government.  Out of all the governmental users the Tennessee Valley Authority (TVA) had the sole job of mapping the Tennessee Valley during the Great Depression.  By the end of the 1930’s the TVA had charted over a million acres and was one of the best mapped regions in the nation.  The knowledge and skills that were acquired by those who were employed in the aerial surveillance field would later be put to use in the Second World War.  Because of their great mapping expertise, the TVA would be assigned to map the coastal areas of the United States in order to prepare for a possible invasion.  Later on, the Army would use the TVA to map Nazi-occupied France. 

By the Second World War, aerial mapping had advanced to the point that it was no longer a daytime activity.  The general uses of aerial mapping in the Second World War, included mapping and damage assessment.  This was important in the fact that it gave military strategists insight on how well something was bombed in order to finish the mission or just go home.  In 1944 the Army would ask an MIT professor to design a flash strong enough to penetrate through the dark but not noticeable enough to be detected by enemy troops.  Harold E. Edgerton had already had the basic concept created by use of a strobe like device that would slow motion down.

In the 1950's President Eisenhower offered to trade aerial reconnaissance information between Russia and the United States.  However, the plan was met with opposition.  Russia declined the offer.  In response, Eisenhower made an agreement between the CIA and the US Air Force to contract with Lockheed Martin to design and produce an aircraft capable of high altitude aerial reconnaissance.  This brought about the creation of the U2.  As a result the first flight over the Soviet Union was on July 4, 1956.  The U2 had the capability to fly higher than any anti-aircraft mechanisms available at the time.  However, in 1960 Francis Gary Powers, a civilian pilot flying a U2 for the CIA was shot down, imprisoned and put on trial in the Soviet Union.

Later in the 1960's, some members of the United States Geological Survey (USGS) would propose to use satellites as a more cost effective solution for aerial surveillance applications.  The USGS was mostly interested in topography, although they acknowledged that there were a wide variety of applications for the technology.  Due in part to the capture of Francis Gary Powers, a satellite program was created in order to better apply surveillance to countries hostile to the United States.  This led to the creation of a number of satellite programs. Among these programs were the Corona and Landsat Satellite Programs, with the Corona Satellite Program being the first satellite program to be created.  The Corona satellite was equipped with two reels of cassette tape.  After the film was exposed to the cassette, the cassette was jettisoned and an aircraft recovered the jettisoned cassette in flight.  It is of interest to note that one Corona mission obtained more information than all of the U2 missions combined.  Some of the information obtained from this Corona mission included surface to air missile sites and other previously unknown air fields.  The Corona program lasted until 1972, when the United States Government began using the Landsat series satellites.

The Landsat satellites were used by the United States Geological Survey, the Department of the Interior, the Department of Defense, and many other governmental organizations.  Although the Corona satellite program was used mostly for military strategic purposes, the Landsat 1 Satellite was used for many non-military applications.  However the military still had access to more information than they did previously from the Corona series satellite.  The Landsat series satellites incorporated two different image sensors.  The most notable of the sensors was the MultiSpectral Scanner System (MSS).  The MSS would prove to be the workhorse of the Landsat Series satellites.  The MSS is important because it records multiple bands of spectral data.  The Landsat series of satellites had seven generations.  The seventh generation is still being used today and is scheduled for use up until 2012.  Advances from the Landsat series include thematic mapping, multispectral scanning and Return Beam Vidicon (RBV). 

One of the biggest mistakes in the Landsat program was privatization of the program.  Previous to the privatization of the Landsat program, imagery was relatively cheap to acquire and readily available.  However, when the Landsat program was privatized, the cost of imagery prices rose over 100%.  For this reason, many users of satellite technology opted for cheaper, lower grade imagery.  During this time, other companies such as Orbimage were trying to find a niche in the remote sensing market through selling satellite imagery.  Orbimage would later be acquired by GeoEye, which would become one of the largest providers of satellite imagery. 

To this date, aerial images acquired by satellite are almost as good as or better than surveys from an aerial platform.  However, the demand for survey from an aerial platform has not diminished to date.  For this reason, technological advances have been made in aerial survey cameras.  Some of these technological advancements include low distortion lenses, forward image motion compensation, the ability to use multiple sensing mechanisms in one unit, and most notably, the digital aerial camera.  "The hardware and software used to transform information from 2D digital imagery into 3D data has allowed the mapping process to become increasingly automated.  Leica Geosystems was the first company to introduce the large format digital camera, the ADS40, in the market in 2001.  The ADS40 produces images that are radiometrically and geometrically superior to images captured by conventional film cameras.  Vexcel, a company founded in 1985 and recently acquired by Microsoft, has also developed UltraCamD Digital Aerial Camera System that delivers large format aerial imagery.  Another such camera is Intergraph's Z/I Imaging DMC (Digital Mapping Camera)." (GIS Development)  Currently Leica has the most advanced camera.  Leica and Microsoft hold the greatest share of the digital aerial camera market. 

Conclusion

Aerial mapping and remote sensing technologies have advanced rapidly over the last eighty years.  The way in which we see the world now is far different than the way in which we used to see the world.  We are able to see on a thermal level, an ultraviolet level, infrared level, and are able to manipulate the information to suit our geographic needs.  Not only have advances to camera technology been important, but also advances to the aerial platforms have been made, including widespread use of satellite technology.  This technology is beneficial to a wide variety of people, from professionals needing accurate information about the surface, to the ordinary person needing directions to the coffee shop courtesy of Google Earth and Google Maps. 

How About a Piece of History

Go ahead and see for yourself.

http://news.google.com/newspapers?id=NGspAAAAIBAJ&sjid=MucDAAAAIBAJ&dq=aerial%20camera%20history&pg=791%2C737112

Aerial Triangulation as Presented by ASPRS

Farm Photography

I would like to thank the United States Department of Agriculture for today's material.  To visit their site just visit http://www.fsa.usda.gov/FSA/apfoapp?area=apfohome&subject=landing&topic=landing. I will also include this link in the useful sites index. The USDA provides an image library and a host of geospatial products.  I found it by googling aerial farm photography.  I decided to check the website out and found it to be informative.  In the meantime, here is a somewhat unrelated photo to entertain your eyes.  By the way, I like cows.