General Actions:
This document outlines the process for the collection of hemispherical canopy photography used at the TERN 'Super Sites'.
IMPORTANT NOTE: Hemispherical canopy photographs are best collected in diffuse lighting conditions, when the sky is uniformly grey (eg. around dawn and dusk when the sun is below the horizon, or on days with 100% cloud cover). The quality of these images for analysis purposes is compromised if taken at other times, particularly around solar noon. If it is only possible to take pictures during sunlight conditions, it is possible to mask out the influence of the sun, but this is not ideal and will bias the gap fraction estimates. Try not to have fluffy clouds in the images either, as the brightness of clouds can reduce leaf cover at the edges of the leaves. In addition, hemispheric photos should not be taken in windy conditions.
The hemispheric photo collection process outlined in this document assumes the photos are taken at intervals along established star transects. Sites should be selected in the manner outlined in the star transects protocol here.
Star transect plots are 100 m in length (50 m radius). 13 photos are taken (1 in the centre of the star transect, 6 half way along each arm ( at the 25 m point) and 6 at the ends of each transect.
The following data must be recorded for data management purposes:
1. Lay out plot
This protocol is designed for data to be collected in conjunction with SLATS star transects. As such the plot should already exist. If data is being collcted independently, then layout plot in the manner outlined here.
2. Take a GPS reading at the centre of the plot.
It is best to use survey-grade differentially corrected GPS if possible because it is important that the gaps within and between trees lines up with the fractional cover estimated from LiDAR. The horizontal error from a handheld GPS can be in the range of of 2 m to 10 m and can cause problems when validating high spatial resolution products, such as airborne LiDAR. If ground control points are available that will be identifiable in both the field and the imagery, these can be used to improve the integration of field and image data through a distance and bearing measurement between the GCP and the centre of the plot.
3. Record site details on field sheet.
Record the following details on the field sheet:
Use a separate sheet for each height/lens combination.
4. Take photos
Take photos at the centre location, then halfway along each of the plots six arms. If the vegetation is sparse or tall, take a further photo at the end of each arm. Make sure all required photo details (photo numbers, height and time) are recorded on the field sheet in the appropriate location.
Camera setup
Ensure the following settings are used for the photographs: