Thursday, December 01, 2022

A new system combines aerial and terrestrial thermal images to study drought in trees

A new system combines aerial and terrestrial thermal images to study drought in trees

This method extracts thermal data from images taken in confined areas of soil and plant canopy, i.e. the layer of branches and leaves formed by treetops. Specifically, cameras take pictures that scan the temperature of both surfaces. The photos, transferred to a computer, record the different levels of heat that accumulate in each part of the tree and show them on a color scale: the coldest areas in the blue range and the coldest in the yellow, orange and red tones. hot area.

Thus, these thermal images allow the evaluation of the temperature of each tree within a plot and in the soil. “This indicator is associated with the degree of stress, so that the higher the temperature of a tree, the greater the stress,” explains study co-author Victoria González Dugo’s researcher at the Institute for Sustainable Agriculture.

To inspect the areas most sensitive to water scarcity, He made the first flight to take pictures under abundantly irrigated conditions in a field of peach trees, and after a few days made a second flight without watering the area.

pictures from the air

To collect the necessary information from the trees and the terrain, they used thermal and multispectral cameras mounted on a small aircraft. A researcher from the Research Center on Desertification told the Discover Foundation on desertification, “This type of instrument has sensors capable of capturing information in different regions of the light spectrum that allow us to calculate various vegetation indices related to plant health and well-being. Huh.” Juan Miguel Ramírez-Cuesta, one of the people responsible for this work.

In particular, these aerial images show the functioning of stomata of leaves, pores on the surface of plants. “When stressed, the tree does not evaporate and becomes hot. That heat is reflected in aerial images focused in treetops and in photographs of leaves taken on the ground,” says Ramírez-Cuesta.

Experts verified that the accuracy of the aerial images makes it possible to identify individual tree crowns and separate soil from vegetation. “This is not possible with other types of low-resolution images such as those offered by many satellites. The information provided by images taken from the ground is more accurate, but it is a specific measurement that is difficult to extrapolate across the plot.” “, explains Ramirez-Cuesta.

The data obtained from the thermal aerial images were processed in the laboratory of Quantitative Remote Sensing Methods (Quantlab) of the Institute of Sustainable Agriculture, led by Pablo Jarco Tejada. There, experts prepared a mosaic with all the images obtained in order to analyze the entire area as a whole.

information from the ground

In the field, they measured the water status of the leaves with pressure chambers. To do this, he isolated a tree leaf in an aluminum bag. After an hour without exposure to the outside, that is, neither sunlight nor room temperature, he made some cuts and placed it in the pressure chamber. “At this point, pressure is applied up to the petiole, an appendage that connects the leaf and the stem, expelling a drop of water. The more pressure you have to apply to remove the water, the more the leaf experiences There will be tension,” Ramirez-Cuesta details.

The results of the study, ‘Assessment of peach tree water status and leaf gas exchange using ground-based air-based thermal imagery’ and published in the journal agricultural water managementrevealed that information from aerial thermal images allows for more accurate tracking than photographs taken from the ground. However, leaf gas exchange is best captured by cameras used in the field.

A New System Combines Aerial And Terrestrial Thermal Images To Study Drought In Trees
The fruit of one of the peach trees controlled in the study.

In this sense, experts advocate a combination of both types of images. “Each one contributes a specific value, so the combined use of the two provides an optimal and more complete result. Portable thermal cameras can capture shady and sun-exposed parts of the canopy independently, from their side view. Thanks for this, but usually only capture one tree per image. However, to compare the different areas used from the wind cover the entire surface”, explains Ramírez-Cuesta.,

Irrigation Strategies

On the other hand, the information provided by these thermal images helps to identify which specific areas of the plot are most affected by water stress, allowing the establishment of more efficient irrigation strategies. “Based on this, the farmer can decide which are the most sensitive points to drought and have sensors installed that serve as warnings of water shortages in the soil,” explains Ramírez-Cuesta.

This study is part of the European project IRIDA, which focuses on the application of innovative remote and terrestrial sensors as decision-making support for water management in agriculture, has received funding from the State Research Agency and FEDER funds.

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