Hyperspectral Flight Planning Requirements

Data Collection

Line-scan cameras integrated in GRYFN systems trigger data collection via either a GPS polygon or GPS flight line coordinates, depending on the sensor manufacturer. In order to trigger data collection, this polygon needs to be created during the flight planning process.

The GPS polygon has a few requirements to collect high quality data consistently:

1. Polygon must be slightly shorter than the Total Area Coverage (Flight Lines) in the direction parallel to flight lines. In summary, the UAV must exit the polygon at the end of a flight line before turning.

   1. During a turn, at the end of a flight line, the UAV speed is unstable and generally lower than the planned flight speed. Because of the fixed framerate of these cameras, the sensor (and therefore UAV) needs time to get up to the proper speed after a turn.

   2. Hyperspectral data is very storage intensive, so it is recommended to not collect data during turns. In addition to sensor pitching, this data is not captured at the correct speed relative to the framerate, and should be excluded from processing.

   3. Exiting the polygon gives the UAV time to get back up to the proper flight speed, as well as resolving the orientation, prior to the sensor re-entering the polygon area and re-enabling data collection.

2. Polygon must be slightly wider than flight lines in the direction perpendicular to flight lines.

   1. This is to ensure any instability in the aircraft, or wind, does not cause the UAV to laterally exit the polygon during the first or last flight lines.

3. From the takeoff location, the UAV/sensor should not enter the polygon as it navigates to the first survey waypoint.

   1. For sensors with vertical components of the polygon, set the minimum altitude of the polygon such that any alignment and navigation to the first waypoint can be done below the polygon

   2. For sensors without vertical polygon limits, ensure the aircraft can easily navigate to the first waypoint without laterally entering the polygon.

It is recommended that the survey flight lines extend beyond the bounds of the GPS polygon/survey boundary by at least 2m for every 1m/s of flight speed, to achieve proper speed and heading before re-enabling data collection.

Therefore, if a flight is planned for 5m/s flight speed, survey flight lines should extend beyond the GPS polygon area by at least 10m. It is also recommended that the buffer of the survey boundary beyond the area of interest be extended for hyperspectral flights beyond the general recommendation for flight planning. A good metric to use is 2m for every 1m/s of flight speed.

In summary, hyperspectral flights should have a survey boundary/GPS polygon setup such that it is larger than the area of interest by 2m for every 1m/s flight speed, and flight lines should extend beyond the survey boundary for an additional 2m for every 1m/s flight speed.

Hyperspectral Panels

In order to correct field hyperspectral data in the post-processing step, calibrated spectral panels are used to employ an empirical line method correction on the raw/radiance sensor data. The panels will be measured in GRYFN Processing Tool from the hyperspectral data cubes. Therefore, the spectral panels must be captured by the sensor while it is airborne.

In order to ensure consistent lighting during collection of the panels, all spectral panels should be visible in a single data cube. To accomplish this, it is best to set up the panels in a row parallel with a planned flight line. Additionally, it is preferred to set the panels up in order of reflectance value in the field to aid with measurements in GRYFN Processing Tool. At certain exposure levels, the brighter targets can look very similar in the raw data cubes; if they are in order then there shall not be the need to guess which panel is which.

In certain instances, the operator may not have access to the survey area to place spectral panels, or there may be no room near the survey boundary. In this case, the spectral panels can be placed near the takeoff location, a flight line can be added before the survey to fly over the panels before heading to waypoint 1, and an additional GPS polygon/flight line can be used to capture the spectral panels.

Multiple polygons for data capture (GRYFN)

Hyperspectral Flight Plan Visualized

The polygon should be wider than the area of interest being flown, but shorter than the flight line length. Polygons should be wider than the flight plan in the perpendicular plane of the flight line (if flying E-W, polygon should be larger than flight plan in N-S direction). The figure below also depicts an example of where and how spectral panels should be placed in the field.

Example with flight lines visible, explained:

• Flight is being flown west to east at 5m/s

  • Area of Interest are the corners of the agricultural field

  • Polygon extends 10m beyond AoI in E-W direction.

  • Flight plan extends 10m beyond polygon in E-W direction.

  • Polygon extends 15m further than flight plan in N-S direction.

Area of Interest, Survey Boundary/GPS Polygon, Flight Lines (GRYFN)