HemiView Forest Canopy Image Analysis System

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HemiView image analysis systemHemiView hemispherical imageHemiView image analysis system in the fieldHemiView image analysis system below tree canopy

Testimonials

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

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

Designed for field use

Images are obtained 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 to ensure it is held horizontally, whatever the mounting angle. The Mount 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 a 20 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.

Specification

 

Image file typesBMP, JPG, TIF, Photo CD.
Lens distortionCan be specified as a polynomial relating zenith angle and radial distance.
Direct light modelSimple atmospheric transmission, with user defined settings.
Diffuse light modelUniform or Standard overcast sky.
Data outputExcel compatible spreadsheet built-in.

Outputs

 

Sky GeometryCentroid, solid angle and pixel count for each sky sector.
Gap FractionProportion of visible sky by sector.
Leaf Area IndexBy sky sector or overall value.
Solar RadiationDirect and diffuse, above and below the canopy, in energy or molar units.
Site FactorsDirect, indirect (diffuse), global.
Time series and SunflecksVisibility 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 correctionFor any orientation of intercepting surface.
Overall valuesMost outputs can be tabulated by sky sector, or aggregated into a single overall whole sky or annual value.

Features

 

Interactive graphical alignment toolPrecise registration of images with the hemispherical co-ordinate system. Compensates for magnetic declination.
Responsive image classificationThreshold intensity discriminates visible and obstructed pixels. The classified image view is updated in real-time.
Multiple and split views on any imageClassified and colour / grey scale views, or separate sections of a large image can be viewed side by side.
Negative imagesPhotographic negatives can be viewed and analysed as positives.
User-defined number of diffuse sky regionsEnables use of custom ranges of zenith and azimuth angle.
Leaf Area of a Single TreeExcel spreadsheet provided with instructions for calculating single tree LAI using HemiView outputs.
Analysis of partial imagesUnwanted parts of images can be ignored by the analysis.
Configurable for site, lens, solar modelUser-defined site, lens and solar model characteristics can be applied to any image by selecting from a list.
Pre-defined lens characteristicsLens equations are provided for current and previous lens types supplied by Delta-T Devices
Results output to Excel compatible workbookAdditional calculations can be performed using standard spreadsheet formulae. Alternatively, workbooks can be saved for further analysis using Excel. Results can be appended to existing workbooks.
User-defined output configurationsThe user can define multiple custom output configurations which can be applied to different images.

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