Dataset Open Access

Spherical forest phenology images - 2017 - Harvard Forest

Hufkens, Koen

Introduction

This is the collected data from the Virtual Forest project with acquisitions from 10min to a base setting of half an hour, for a total of roughly 13K images. The virtual forest project ran from late 2016 until early 2018 in Harvard Forest, Petersham, MA, USA. The project took spherical images of the forest canopy for an interactive online installation. Data collected may have research purposes outside the scope of the original outreach project.

Methods

Location

The camera was located in Harvard Forest, Petersham, MA, USA. The exact location of the camera was 42.535685326, -72.189706396 decimal latitude and longitude and an elevation of 337 m (as determined by high precision GPS).

Hardware & Software

The setup consisted of a Ricoh Theta S camera, tethered via USB to a Raspberry pi. Images were taken on a varying time schedule (for visualization purposes), but guaranteed a half hourly acquisition. Here, only the half hourly data is reported. Images were collected at both a normal (exp0) and 2-stop underexposed value (exp-2000). Only the full growing season of 2017 is included in this dataset. A  detailed description, with updated hardware (Ricoh Theta V) is provided in the photosphere repository.

Post-processing

The naming convention of the files is compatible with the processing toolchain of the PhenoCam US network. Images were reprocessed from equirectangular to hemi-spherical images (top and bottom), to reduce the file size. The top of the image is approximately north in both up and downward looking orientations.

Processing of the images for colour indices is therefore easily accomplished using the software of this project. These include the vegindex python package to convert image data to colour indices. Data were pre-processed for a lower, mid and high canopy region of interest (30 degree bands) and the understory of the forest. I report 3-day agregated values. Transition dates can be extracted using my phenocamr R package.

Data structure

The data is delivered as a large compressed file. After extraction several folders with data are provided. The virtualforest_canopy* folders include canopy data, looking overhead. The 'underexposed' folder was not processed for colour indices but includes images which are 2 stops underexposed as common when using hemi-spherical images to determine a leaf area index (LAI). These images can therefore be used within this context. The virtualforest_understory folder includes all downward looking images (matching those in the virtualforest_canopy folder. Colour indices for the understory were calculated.

When colour indices are calculated the results can be found in the ROI folder, following the structure as described in the 'vegindex' python package used for processing.

Additional information

Please contact us at info@bluegreenlabs.org if you have any questions regarding this data. Equirectangular data files equivalent can be provided upon request, file size prohibits easy sharing however.

I've been indebted to the Harvard Forest staff, for helping me with practical issues and the hosting arrangement, and dr. Andrew Richardson for project time.
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