Data Standards for Detailed Aerial Surveys

In areas where more spatially accurate data is required to direct operational activities, detailed aerial surveys may be done. These surveys are mainly done to detect bark beetles. They are performed by forest district staff and/or licensees using rotary or fixed-wing aircraft, often using Global Positioning System (GPS) navigation equipment.

This detailed survey data has occasionally been incorporated into the provincial aerial overview surveys, in limited areas when it is the only source of aerial survey data for a given area and year. The detailed aerial surveys should also follow these core digital mapping standards, to simplify summaries within regions and districts.

Helicopter/GPS (heli-GPS) fixed surveys are the current best practice for conducting accurate, timely and cost-effective detailed aerial surveys.

This standard provides GPS coordinates for detected centres of red attack with a horizontal accuracy of approximately 20 m.

Errors of commission – identifying a centre of red attack where there is none

  • Extremely low (<5%);

Errors of omission – identifying a non-infested site when it is infested

  • Unknown. Depend on the survey effort in a particular area. If an area is covered completely, errors of omission are probably less than 5%, meaning that more than 95% of the infested sites are located.

Image resolution – the level of accuracy consistent with the helicopter/GPS surveys is obtained with images produced at 1 m pixel (50 cm is ideal) resolution.

In general, the aerial detection method must be able to identify both the number and location of individual red tree crowns, and the species of tree killed.

The final product of this mapping exercise shall be a map (and GIS files) showing:

  • The location(s) of red attacked trees, pest codes, and tree counts (if spots, +/- 10%) or severity (if polygons +/- 5%) with GPS coordinates adequate to allow ground crews to find the centre of an infestation site with +/- 25 m accuracy
  • Infestations will be depicted as either points (spots) with tree counts or polygons with infestation severity (in 10% increments)
  • The perimeter of area covered by the survey

The estimated unit cost for the standard detailed survey (helicopter/GPS) is $0.15/ha (product = map delivery).

GPS Standards

Aerial Surveys within +/- 20 m horizontal accuracy. Positional accuracy for bark beetle detection usually falls under the category of "non-critical" since the allowable horizontal errors for collecting point data can be greater than 10 m (as per B.C. Standards and Specifications and Guidelines for Resource Surveys Using Global Positioning System (GPS) Technology Release 3.0 - Section E - Autonomous GPS Guidelines).

Thus, at a minimum, locations recorded by hand-held autonomous GPS receivers (recreational use receivers) provide an acceptable level of accuracy when under clear tracking conditions. As noted in the guidelines above, use these devices with caution to minimize error. In most cases, the objective of the survey is to locate the "infestation centre" within 25 m, and not the precise location of each infested tree within the infestation center.

To improve accuracy, surveys should use differential GPS or high-end autonomous GPS receivers whenever possible.

Spatial Data Standards for Detailed Aerial Surveys

The aerial overview digital data standards were modified to accommodate more detailed data obtained from operational aerial surveys, to archive the detailed information in a standard format. 

Detailed Aerial Overview Digital Data Standard

Detailed digital data standards are the same as the basic standard.

Database Codes

NODE_NUM REGION DISTRICT YEAR

MAP_NUM

FHF

SEVERITY

POLY_AREA

SPOT NUM_TREES SPOT_AREA  

The only difference for detailed surveys is that the SEVERITY attribute is modified to designate the more precise estimate of percent infested within polygons sketch mapped, extracted from remote sensing or recorded on a GPS. The severity codes are a single digit, and are stratified by increments of 10%.

Severity Codes

SEVERITY CODE

SEVERITY RANGE

0

0.1 to 10%

1

11 to 20

2

21 to 30

3

31 to 40

4

41 to 50

5

51 to 60

6

61 to 70

7

71 to 80

8

81 to 90

9

91 to 100

 

Minimum Metadata Specifications for All Provincial Aerial Survey Data

Metadata requirements are the same as the aerial overview digital data.

All IGDS and ArcGIS data will be in the following format:

Projection: Albers Equal Area
Datum: NAD 83
Units: Metres
Spheroid: GRS 1980
1st standard parallel: 50 0 0.000
2nd standard parallel: 58 30 0.000
Longitude of central meridian: -126 0 0.00
Latitude of true scale: 45 0 0.000
False easting (metres): 1000000.00000
False northing (metres): 0.00000