Table 1 A comparison of different low-cost NDVI camera systems, highlighting the pros/cons of each system, and indicating the main advantage of the NDVIpi system described here

[59]

£360

Two-camera seperation of Red/NIR; off-the-shelf consumer cameras; good quality optical filter

2 or Less references

NDVIpi uses 6 references to account for non-linearity of consumer cameras; Lower-cost optical filter is used without detriment to accuracy

[60]

£594 (excluding optical filters)

Two-camera seperation of Red/NIR; off-the-shelf consumer cameras; good quality optical filter; doesn't require calibration targets; vignetting correction

Requires on-site downwelling spectrometer

Programmable camera control; low-cost optical filter; can be customised and integrated with other systems; affordable reference targets

[47]

£545

Dual-band optical filter on a single camera; multiple references

No programmable control of camera, not easy to integrate with other systems

Programmable camera control; low-cost optical filter; can be customised and integrated with other systems

[46]

£100 (excluding filters)

Two versions, one with a low-cost optical filter and one with a dual-pass optical filter; multiple references; single camera (no need for alignment)

No programmable control of camera. Leakage of NIR and Red (low-cost optical filter) due to single camera

Programmable camera control; low-cost optical filter; can be customised and integrated with other systems; low-cost filter; dual-camera to present NIR leakage

[18]

£110

Multiple References; Calibration to account for non-linearity; Two-camera seperation of Red/NIR

Requires camera modification

Programmable camera control; low-cost optical filter; can be customised and integrated with other systems; requires assembly

[19]

–

Two-camera seperation of NIR and red; good quality optical filters

No calibration

Calibration methodology and multiple references; Lower-cost optical filter is used without detriment to accuracy

[61]

£325 (£406 for reference targets)

Multiple References; Calibration to account for non-linearity; One camera with high quality optical filters

Programmable camera control; low-cost optical filter; low-cost reference targets; can be customised and integrated with other systems; calibration inherently accounts for gamma; correction (thus any camera can easily be used in the NDVIpi without requiring determination of the gamma correction)

[62]

£200 (excl. filters)

Two-camera seperation of NIR and red; good quality optical filters

Requires on-site downwelling spectrometer

Calibration methodology and multiple references; Lower-cost optical filter is used without detriment to accuracy; an be customised and integrated with other systems

[63]

£60 (excl. filters)

Raspberry Pi based; good quality optical filters; single camera system

2 or Less references

NDVIpi uses 6 references to account for non-linearity of consumer cameras; Lower-cost optical filter is used without detriment to accuracy

[48]

£785

Good quality optical filters; single camera system

2 or Less references

Low-cost reference targets; can be customised and integrated with other systems; calibration inherently accounts for gamma; correction (thus any camera can easily be used in the NDVIpi without requiring determination of the gamma correction)

[12]

£968

Narrowband filters over CCD camera; Good quality optics; Two camera seperation; Very similar to commercial cameras

Off-the-shelf components

[64, 65]

 ~ £200

Low-cost filters

Blue channel used for visible wavelengths; no hard seperation of VIS/NIR

Red wavelengths for NDVI calculation; two camera seperation; Programmable camera control; Six references

[22]

£712

Single Camera; No optical filters; algorithmically seperates NIR and visible images

Lower cost