- Model HemiView HEMIv9 - Forest Canopy Image Analysis System

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The HemiView canopy image analysis system provides the hardware and software needed to acquire and analyse hemispherical images of forest canopies.

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Hemiview - Canopy Image Analysis System

  • Analyses Hemispherical Images
  • Calculates canopy structure parameters and solar radiation indices
  • Predicts radiation levels beneath canopy

Designed for field use
Photographs are taken looking upwards from beneath the plant canopy, or from the forest floor, using a 180° fisheye lens and a high resolution digital camera. Uniform sky conditions are required, such as exist just before sunrise or sunset, or when the sky is evenly overcast. The digital camera is mounted in a Self-levelling Mount, type SLM9, to ensure it is held horizontally, whatever the mounting angle. The SLM9 also provides markers for the horizon and north-south axis, to assist with image alignment.

Powerful image analysis
The HemiView canopy image analysis system processes the image data file to obtain information about canopy structure e.g. Leaf Area Index (LAI), gap fraction and distribution of openings. By combining this information with radiation data, HemiView can predict the PAR intercepted and the radiation levels beneath the canopy. The software also calculates radiation indices, canopy indices, suntrack overlay and the direct and diffuse site factors; advanced graphing facilities help visualise the data. Data can be exported in several common formats.

The leaf area of a single tree can be calculated from HemiView outputs by using an Excel spreadsheet provided with the software.

Constant improvement
The HemiView canopy image analysis system is frequently updated to take advantage of improvements in digital camera technology. The latest evolution, adding an even higher resolution digital SLR camera to the system, significantly improves HemiView's performance. Resolution can be the key to accurate analysis of hemispherical photographs, which is why we now supply an 18 megapixel SLR CMOS camera. The camera comes complete with a fibre optic flash transfer assembly (to illuminate the north/south image markers) and memory card.

A matching high quality fisheye lens and redesigned camera mount have also been introduced. The camera mount is considerably lighter than earlier versions, with improved the ergonomics. We have also introduced a new protective case that provides a safe and convenient way to store and transport the camera, lens and mount.

Upgrades
Please contact Delta T Devices for information on upgrading older HemiView models to the latest specification.

Leaf Area Index (LAI) in low canopies
HemiView is ideal for analysing and and characterising canopy cover in forests and woodland. However, for low regular canopies such as crops, the Delta-T SunScan System is the correct choice.

  • Image file types: BMP, JPG, TIF, Photo CD.
  • Lens distortion: Can be specified as a polynomial relating zenith angle and radial distance.
  • Direct light model: Simple atmospheric transmission, with user defined settings.
  • Diffuse light model: Uniform or Standard overcast sky.
  • Data output: Excel compatible spreadsheet built-in.

Outputs

  • Sky Geometry: Centroid, solid angle and pixel count for each sky sector.
  • Gap Fraction: Proportion of visible sky by sector.
  • Leaf Area Index: By sky sector or overall value.
  • Solar Radiation: Direct and diffuse, above and below the canopy, in energy or molar units.
  • Site Factors: Direct, indirect (diffuse), global.
  • Time series and Sunflecks: Visibility of the solar disc (penumbral effects) and solar irradiance on chosen days, sampled at user-defined intervals or summarised as a sunfleck sequence.
  • Optional Cosine correction: For any orientation of intercepting surface.
  • Overall values: Most outputs can be tabulated by sky sector, or aggregated into a single overall whole sky or annual value.

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