Georeferencing oblique PhenoCam imagery

Abstract

The high temporal and spatial resolution of ecosystem data captured by tower-mounted PhenoCams have established these instruments as fundamental tools in phenological studies and positioned them as a critical mid-step between airborne or spaceborne and in-situ data in ecological research. However, adding spatial precision can further expand PhenoCam network applications and attract more users, such as drawing more phenological scientists to the near-surface remote sensing research field. In this study, a georeferencing approach was established to enhance research infrastructure for PhenoCams. Advanced photogrammetric techniques were applied to the camera field of view to geo-enable all pixels, tying them to their location on Earth and adding more usable information to datasets in addition to the current “region of interest” (ROI) level data. The georeferencing method is presented along with the photogrammetric equations that enable going from object space coordinates (3D) to image space coordinates (2D). This method was tested and demonstrated on PhenoCam data at Ordway Swisher Biological Station (OSBS), located in Melrose, Florida, USA. Statistical and sensitivity analyses show that projected pixel-location can be as accurate as 1.5 pixels RMSE for the presented case study, corresponding to object space accuracy of 10 cm, 20 cm, and 30 cm at distances of 100 m, 200 m, and 300 m, respectively. In addition, geo-located PhenoCam data at OSBS was co-located with Moderate Imaging Spectrometer (MODIS) data and characterized. These results demonstrate that the techniques presented reliably provide additional data from PhenoCams that are useful for ecosystem-level studies. By providing each pixel’s absolute location corresponding to its place in the real world efficiently, this research introduces a higher degree of spatial precision to every phenological observation from the PhenoCam at OSBS. This presentation of reproducible steps and analysis facilitates implementation for other PhenoCam data as well as other obliquely mounted cameras.