Small Format Photography by helicopter in Western Colorado
by Rick Moran, firstname.lastname@example.org (2006)
ES 555 Small format aerial photography from Emporia State University
In western Colorado a number of newer gas fields are being developed. Computer automation is used to capture data and allow remote control of the operations. For this to happen a computer network must be established to allow communications between wells locations, facilities, and a central office. The communication network is dependant on installing towers with dishes and associated electronics to create a wireless network tied into existing interstate communication lines. Many of the gas fields are located in mountainous areas where accessibility can be a significant issue. One such field, scattered over a 60 square mile area, was analyzed for a computer network by an iteration of reviewing topographic maps, and by multiple site visits by vehicle and a helicopter flight.
During the helicopter flight small format aerial photography, SFAP, was used to assist in selecting from several proposed communication tower sites. More rigorous large format photography was unnecessary. Satellite images did not include current roads and lacked sufficient resolution. Also photographs at oblique angles were needed to clarify line of site between locations.
A 5 mega pixel camera was used for all photographs. The mounting mechanism consisted simply of holding the camera with both hands out a small window on the side of the helicopter. The view finder could only be poorly seen as photo's were taken. Air speeds above 30 knots placed the camera at risk of being dropped. Due to the helicopter skids below, vertical photography was not possible. Photographs were taken at near vertical angles of 10 to 20 degrees or high oblique angles at ~80 degrees to horizon. In total 130 photographs were taken from the air and 110 from ground level.
Photographs were downloaded unto a laptop during flight to identify image problems. The early photographs showed a slight hazy image would occur shooting through the Plexiglas. Also helicopter skids were appearing during vertical photographs. Along with GPS, Topo! software containing USGS topography maps was loaded unto a laptop for flight navigation. By having the laptop on board it allowed target locations to be changed in flight along with properly identifying ridges.
A series of 17 photographs were taken of a valley from ~2500 feet above. The valley floor averages 600 feet wide wide at the bottom of a 2300 feet deep canyon. Elevations at the canyon bottom drop from 6700 feet on the left to 5800 feet on the right side. Each individual image brightness was adjusted in Photoshop then 14 were selected for a mosaic assembled in PTGui. Control points for the image merging were selected along the valley floor. The limitations of PTGui were noticed as the various camera tilts changed in the flight along with the elevation change in the valley. Even with control points carefully picked it was difficult to create a really good stitched mosaic. SnagIt was used to resample some images to reduce file sizes for web presentation. This was particular useful for the detail blowups and retaining a larger image.
After the the valley mosaic was created 24 GPS coordinates with a hand held were taken along the road to perform a resample in IDRISI. But unfortunately the conversion to a UTM coordinate system wasn't completed due to difficulties converting the file from RGB24 to the required RGB8 format. The mosaic image was degraded from the original 68 Mb file size with NIIRS of level 7 to a smaller .6 Mb file with NIIRS of level 5 suitable for a web page.
The pixel resolution varies from 8 inches to 10 inches dependant upon the camera height. Smaller linear features are identifiable. An example is a temporary 4" diameter flow line lying on the ground the length of the valley. The bright yellow color contrasted against the green sage brush made it visible along the entire length.
The mosaic contained 3 overlapping photographs from which a water tank and emergency spillover containment barrier were extracted. The ground was leveled flat for the tank which made it a suitable target to better understand the parallax occurring. The primary tank is 10' x 20' and the secondary containment barrier is 3' x 30' x 50'. A small yellow valve containment housing on the top edge of the containment barrier is 2' in diameter.
Image 1: containment barrier 30 x 65 pixels, primary tank 22 pixels height, tilted 42 degrees
Image 2: containment barrier 30 x 73 pixels, primary tank 18 pixels height, tilted 30 degrees
Image 3: containment barrier 32 x 70 pixels, primary tank 20 pixels height, titled 0 degrees
Ground level close up of the tanks taken from opposite side.
Single photographs were taken through the front of the windshield of the helicopter at key locations. A slight hazy image resulted, but permitted the view finder to be used.
High angle oblique photo of one valley. Without a helicopter access from the valley floor to the mesa on top 1/2 mile away is a 70 mile, 2 hour drive followed by a 2 mile hike.
Except for IDRISI, the same image processing software was used on ground based photographs. At promising locations for communication towers 10 to 12 photographs were taken to create panoramic views. Those views were reviewed in detail to confirm the visibility of a distant hill top or a building in the valley. In this 360 degree image the valley floor is 2300 feet down and distant ridges 400 feet higher.