Floral infrared emissivity estimates using simple tools

Michael J M Harrap*, Sean A Rands

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

5 Citations (Scopus)
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Floral temperature has important consequences for plant biology, and accurate temperature measurements are therefore important to plant research. Thermography, also referred to as thermal imaging, is beginning to be used more frequently to measure and visualize floral temperature. Accurate thermographic measurements require information about the object’s emissivity (its capacity to emit thermal radiation with temperature), to obtain accurate temperature readings. However, there are currently no published estimates of floral emissivity available. This is most likely to be due to flowers being unsuitable for the most common protocols for emissivity estimation. Instead, researchers have used emissivity estimates collected on vegetative plant tissue when conducting floral thermography, assuming these tissues to have the same emissivity. As floral tissue differs from vegetative tissue, it is unclear how appropriate and accurate these vegetative tissue emissivity estimates are when they are applied to floral tissue.


We collect floral emissivity estimates using two protocols, using a thermocouple and a water bath, providing a guide for making estimates of floral emissivity that can be carried out without needing specialist equipment (apart from the thermal camera). Both protocols involve measuring the thermal infrared radiation from flowers of a known temperature, providing the required information for emissivity estimation. Floral temperature is known within these protocols using either a thermocouple, or by heating the flowers within a water bath. Emissivity estimates indicate floral emissivity is high, near 1, at least across petals. While the two protocols generally indicated the same trends, the water bath protocol gave more realistic and less variable estimates. While some variation with flower species and location on the flower is observed in emissivity estimates, these are generally small or can be explained as resulting from artefacts of these protocols, relating to thermocouple or water surface contact quality.


Floral emissivity appears to be high, and seems quite consistent across most flowers and between species, at least across petals. A value near 1, for example 0.98, is recommended for accurate thermographic measurements of floral temperature. This suggests that the similarly high values based on vegetation emissivity estimates used by previous researchers were appropriate.
Original languageEnglish
Article number23
Number of pages20
JournalPlant Methods
Issue number1
Publication statusPublished - 25 Feb 2021

Bibliographical note

Funding Information:
MJMH was supported by a Natural Environment Research Council studentship within the GW4 + Doctoral Training Partnership (studentship NE/L002434/) and a Bristol Centre for Agricultural Innovation grant to SAR. The funding bodies played no role in the study design, data collection, analysis, and interpretation or the writing of this manuscript.

Funding Information:
The authors would like to thank Natasha de Vere, Laura Jones and the National Botanic Garden of Wales for use of their facilities; as well as Sue Holwell and the University of Bristol Biology Teaching Laboratory for loaning of equipment.

Publisher Copyright:
© 2021, The Author(s).


  • Infrared thermography
  • Angiosperms
  • Floral temperature
  • Emissivity
  • Thermal imaging


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