The Contribution of Airborne Data Collection on Electric Utility Vegetation Management

Data Definition
Once the decision is made to assess vegetation within a right-of-way, many techniques and technologies can be applied to gather raw data. In addition to capturing data, attribute data fields must be established to provide the most useful information to best manage the vegetation under and adjacent to the transmission network. Attribute selection varies from company to company and by regional restrictions. There are several attributes which most utilities inspect .(see table 1) After decisions have been made defining the focus within the transmission right-of-way, an appropriate technology is chosen to collect and store the database. Traditionally, all inspection work was conducted by surveyors on land. -However, the new technologies today include hand-held computers, pen-based computers, back-pack GPS units, digital cameras, and laser range finding devices.

Table 1: Standard Transmission Inventory Data Fields and their Attribute Values (6)

Pole Material	Wood, concrete, steel, latice
Construction Type	Single, H-Frame, 2 pole, 3 pole, tower
Insulator Material	Porcelain, polymer, glass, mixed 1
Guy Wires	Yes, no - - -
Cross Arms	Wood, steel
Stub Poles	None, one, two
Bird Discourages	Yes, no 1
Marker Balls	- Yes, no
Substation Attributes	Client defined 1
Tree Species	Pick list from regional species list
Tree Count	Integer
Tree DBH	Diameter at breast height
Tree Condition	Percentage value based on ISA (International Society of Arboriculture) rating
Tree Maintenance Prescription	Type of trim recommended
Brush	Brush type vegetation (not construed as trees)

Drawbacks of implementing ground units to collect transmission right-of-way data range from consistency issues to production monitoring. The most effective way to canvas the hundreds of miles of transmission line is to distribute line sections evenly among data collectors. When implementing global positioning systems technology, there is no variance in how trees and structures are located. With regards to attribute data, however, each person views and prescribes slightly different trim types and conditions of trees and brush. This lends itself to inconsistent data. Another key issue is travel and planning logistics. Many times these transmission easements lie on such rugged terrain that each collector must be equipped with four wheel drive vehicles and a means for safe communication. No amount of planning can take into consideration unpredictable dangers along the line such as poisonous snakes, mountain lions, and wild dogs. When inspecting areas with a reputation for wild animals or hazardous terrain, two collectors work together. At best, an inspector can patrol only seven to ten miles of line per day.(7) Costs associated with lodging and meals for long stays impact inventory projects significantly.

Mission Planning
The ideal mechanism for obtaining transmission line and vegetation data is the combination of airborne sensors technology with military precise ground control efforts. A myriad of factors impact flight mission planning. Weather forecasts are taken very seriously as they can make or break a flight mission. Airplane payload also plays a part in the planning process. Generally a representative from the utility company is required to observe each flight. This person’s weight can adversely affect the aircrafts ability to maintain steady altitudes. The number of collection days per job is decided during mission planning. In contrast to ground collection, an airborne unit can survey up to 900 line miles per day. Based upon the most current weather forecasts, the project manager will make a conservative estimate on the number of days an aircraft will need to be accessible to the contract. Mission planning software also assists each team before a mission. This defines all parameters for the survey mission, digitized flight lines, pilot guidance information, control commands, and settings for sensor systems. Each flight may be optimized by setting customized path width or flight height. In this way both the appropriate timing and the optimal shape and size of the survey area can be chosen.