FR3101159A1 - Estimation of the leaf area by means of a mobile radar within a cultivated plot - Google Patents

Abstract

The invention relates to a method for determining the leaf area of a cultivated plot, by means of a mobile radar unit (1) positioned at the height of the crops in the plot, said radar unit being in communication with a processing unit. configured to implement steps of: - E1) emission of continuous waves modulated in frequency in the direction of the field by means of the radar unit, the radar unit (1) illuminating a determined zone (z) of the field ; - E2) obtaining at least one radar image of the cultivated plot (20) by means of the radar unit (1), said image consisting of voxels or pixels each comprising a level quantifying a quantity of waves reflected by the crops (5) of the plot; - E3) processing of the acquired image to obtain at least one parameter indicative of the leaf area of the plot. Figure for the abstract: Fig. 1

Description

Estimation of the leaf area using a mobile radar within a cultivated plot

GENERAL TECHNICAL FIELD AND STATE OF THE ART

The invention relates to radar imagery applied to agriculture and in particular to the field of fruits and vegetables for which the growth of vegetation in a plot has an impact on the photosynthetic activity of the harvest provided by the plot.

And the invention finds particular application in the wine sector and in the work of the vineyard.

In the agricultural field and in particular wine-growing, operators commonly need to optimize the leaf/fruit ratio of their plots in order to improve the quality of the grapes at harvest (see in this respect the article by Thierry Dufourcq, "Le rapport leaf/fruit" - http://www.vignevin-occitanie.com/fiches-pratiques/le-rapport-feuilles-fruits/.

In particular, it is interesting for farmers to be able to quickly, easily and accurately collect data allowing them to assess the photosynthetic activity of their plots and the potential for ripening.

PRESENTATION OF THE INVENTION

The invention proposes to estimate the leaf area of a plot. Such a surface makes it possible to deduce the photosynthetic activity of the plot and the potential for ripening.

To this end, the invention proposes, according to a first aspect, a method for determining the leaf area of a cultivated plot, by means of a mobile radar unit positioned at the height of the crops of the plot, said radar unit being in communication with a processing unit configured to implement steps of:

E1) emission of continuous waves modulated in frequency in the direction of the plot by means of the radar unit, the radar unit illuminating a determined area of the plot;

E2) obtaining at least one radar image of the cultivated plot by means of the radar unit, said image consisting of voxels or pixels each comprising a level quantifying a quantity of waves reflected by the crops of the plot;

E3) processing of the acquired image to obtain at least one parameter indicative of the leaf area of the plot.

The invention, according to a first aspect, is advantageously completed by the following characteristics, taken alone or in any of their technically possible combination:

- the method comprises a step E4) of moving the radar unit within the plot so as to obtain images of the entire plot, the method comprising, for each position, of the radar unit a step E5) repeating steps E1) through E3);

- at least one parameter indicative of the leaf area is: e _avg defines as being the average value of the levels of all the pixels/voxels of the image; and/or N _e>eref defined as being the number of pixels/voxels for which the level is greater than e _ref ;

- the radar image is multidimensional and includes at least two of the following spatial dimensions: the depth of the area illuminated by the radar unit, the height of the illuminated area, the elevation, the width of the illuminated area and the azimuth .

The invention proposes, according to a second aspect, a radar image processing system comprising:

. a mobile radar unit comprising a radar configured to acquire at least one image of the cultivated plot, said radar operating in the frequency modulated continuous wave domain;

. a processing unit in conjunction with the radar unit and configured to implement steps of:

- E1) emission of continuous waves modulated in frequency towards the plot by means of the radar unit;

- E2) acquisition of at least one image of the cultivated plot by means of the radar unit, said image consisting of voxels or pixels each comprising a level quantifying a quantity of waves reflected by the crops of the plot

- E3) processing of the acquired image to obtain at least one parameter indicative of the leaf area of the plot.

The invention, according to the second aspect, is advantageously completed by the following characteristics, taken alone or in any of their technically possible combination:

- it comprises a unit for moving the radar unit within the plot, the processing unit being further configured to control the movement E4) of the radar unit within the plot and to repeat for each position of the radar unit steps E1), E2) and E3);

- the radar unit is configured to emit waves in a frequency band between 24 and 125 GHz, preferably between 24 and 122 GHz, preferably at 24 GHz/

The invention, according to the third aspect, proposes a computer program product comprising code instructions for the execution of a method according to the first aspect of the invention, when the latter is executed by a processor.

PRESENTATION OF FIGURES

Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and not limiting, and which must be read in conjunction with the appended drawings in which:

FIG. 1 illustrates an environment for implementing the invention;

FIG. 2 illustrates a radar unit illuminating a plot in the context of the invention;

FIG. 3 illustrates steps of a method according to the invention;

FIG. 4, at the top, illustrates images of plots and at the bottom the radar image corresponding to a vine of these plots;

FIG. 5 illustrates the variations of characteristic parameters of the leaf area during the growth of the vines.

In all the figures, similar elements bear identical references.

DETAILED DESCRIPTION

In relation to FIG. 1 and FIG. 2 , a system 10 for processing radar images of a plot comprises a radar unit 1 making it possible to acquire two-dimensional (2D) or three-dimensional (3D) images of a given area, in particular of a 20 cultivated plot comprising 5 vines.

The radar unit 1 comprises a radar 11 operating in the millimeter wave or microwave domain and at wide frequency band. Preferably, the radar 11 operates in the frequency -modulated continuous wave (FMCW) domain. Furthermore, the radar unit 1 comprises a focusing unit 12 which makes it possible to focus the electromagnetic beam emitted by the radar. The beam scans the scene using a mechanical device (mechanical scanning) or an electronic device (electronic scanning), or a hybrid device that is both mechanical and electronic.

In operation, the radar unit 1 is preferably arranged at ground level so as to be able to produce radar images of the crops on the plot. We understand here that the radar unit 1 is at the height of the crops (and not above as in the widely documented and old techniques of satellite or airborne radar imagery, the limitations of which are well known).

In a complementary manner, the system further comprises a unit 13 for moving the radar configured to move the radar in the cultivated plot from one position to another so as to obtain images of at least one crop for each position of the radar, the radar moving in the cultivated plot from each position and then performing at least one acquisition from each position by successively illuminating different areas of the plot.

Thus, in order to allow the displacement of the radar unit 1, the latter can be placed on a vehicle or mobile robot (remotely controlled or motorized with driver of the Quad type, in any event, the vehicle must be adapted to move around the cultivated plot). The radar is equipped with a device allowing to know precisely its displacement in order to take it into account during the processing of the image.

The radar unit 1 is electronically or mechanically scanned and moves (translational movement, for example) in order to increase the spatial resolution of the measurement. This radar imaging technique is known as the SAR ( Synthetic Aperture Radar ) method. Although very widely used by satellite or airborne imagers, this method has never been applied to the estimation of the leaf surface from a ground radar in millimeter waves or microwaves and moving in the furrow of a plot (i.e. at crop height).

The use of the radar unit 1 also has the advantage of being without contact with the crops present on the cultivated plot so that they are not damaged during the various measurements.

The system further comprises a processing unit 2 configured to implement steps of a method for estimating the leaf area which makes it possible to characterize the photosynthetic activity of a cultivated plot. . This method will be described below. The processing unit 2 is in wired or wireless connection with the radar unit 1.

Indeed, the Applicant has noticed that the leaf area of a cultivated plot is correlated with the radar echoes of the illuminated surface in the cultivated plot.

In particular, the Applicant has noticed that it is for FMCW waves emitted at a frequency greater than or equal to 24 GHz that the correlation is strong.

In a complementary manner, the system 10 comprises a memory 3, which makes it possible to store images obtained by the radar 1 and software which controls the processing unit 2 so that it implements the method. The system also optionally comprises a tool 4 for interaction with a user allowing an operator to view acquired images, enter data or configure the software. This is for example a keyboard associated with a screen.

In connection with FIG. 3 , from an initial position, the radar unit 1 E1) emits frequency-modulated continuous waves in the direction of the plot and as such illuminates an area of the plot.

The electromagnetic waves backscattered by the illuminated surface of the plot are then acquired (step E2).

The processing unit 2 then reconstructs a 2D or 3D radar image of the plot. The reconstructed 2D or 3D image is made up of pixels (2D) or voxels (3D), each comprising a level of radar echo in the plot.

Thus, the radar image obtained is multidimensional and includes at least two of the following spatial dimensions (see figure 2): the depth of the area illuminated (in the direction y) by the radar unit 1, the height (in the direction z ) of the illuminated area, the elevation (angle θ), the width (along the direction x) of the illuminated area and the azimuth (angle φ).

Then, from the image obtained, at least one parameter indicative of the leaf area of the plot is obtained (step E3).

Radar unit 1 is then moved either remotely or by an operator (step E4) and at least one image of the area from the new position of radar unit 1 is acquired.

By successively moving the radar unit 1 from position to position, the entire plot is imaged.

Several displacement configurations are possible:

- according to a first configuration: the radar is stationary and placed in front of a set of crops (for example vines), the latter then performs a mechanical or electronic or both mechanical and electronic scan to obtain a radar image of the area . Once the image has been obtained, the radar will then be moved a few meters (for example, along a furrow), a new image will then be obtained and so on. This configuration is said step by step ;

- according to a second configuration: the radar unit 1 is mobile and placed on a moving vehicle (for example, along a furrow): the scanning radar unit 1 will illuminate the area while undergoing the jolts associated with the movement of the vehicle carrying the radar. This configuration is called dynamic .

As mentioned above, the various radar images obtained make it possible to obtain indicative parameters (i.e. statistical estimators constructed from the radar echo levels in each voxel of the 3D image) of the leaf surface.

A first parameter indicative of the leaf area is the statistical estimator denoted e _avg and defined as the mean value of the radar echo levels of all the pixels of the D2 image or voxels of the 3D image. This is a global indicator representing the average echo level of the scene interrogated. Compared to a measured reference scene, the average echo level e _av increases with the development/growth of the leaves. This average level is compared with the maximum value of the distribution denoted e _ref which serves as reference echo level for all the measurements. This value depends on the measured reference scene and the signal-to-noise ratio of radar unit 1.

A second parameter indicative of the leaf area is the statistical estimator denoted N _e>eref and defined as the number of pixels/voxels for which the radar echo level is greater than the reference echo level e _ref. This second indicative parameter does not represent an echo level, but a spatial quantity of surface (2D) or volume (3D) of occupation of the echo levels greater than the value given by e _ref.

Figure 4 (top) shows plots in different months of the year: May, June and July in this case. These plots have different amounts of leaves. Also on this figure (bottom), 2D radar images are reported for a given depth of these same plots and for different months of the year: the gray level represents the echo level, the stronger the echo and the lighter the gray color. As expected, the light gray areas expand as the foliage of the plots grows.

Therefigure 5illustrates the distribution of echo levels according to the number of voxels as well as the indicator e_ref.The reference value e_ref=-61.0dB (± 0.5 dB) is the maximum value of the distribution (i.e. the highest peak in voxels) in May of the plot (i.e. in the case where there is little foliage). The values of the parameter e_averageabsolute and relative with respect to e_refare reported in the table below. The increase in the value of e_averageis linked to the increase in the level of radar echo associated with the development of the leaf area of the plot's measured plants.

For the reference threshold e_ref=61.0dB, indicative parameter N_e>erefincreases significantly as plot foliage increases: N_e>eref= 9370 voxels in May, N_e>eref= 16300 voxels in June and N_e>eref= 18770 voxels in July. These values are represented on the distribution function of thefigure 5and are reported in the painting. Each voxel representing a volume resolution of the measured scene, the increase in the number of voxels beyond the reference threshold e_refis characteristic of the increase in the levels of radar echoes distributed in the measurement volume.

e _avg e _av - e _ref N _e>eref May -64.0dB -3.0dB 9370 voxels June -56.3dB 4.7dB 16300 voxels July -54.1dB 6.9dB 18770 voxels

Claims (8)

Method for determining the leaf area of a cultivated plot, by means of a mobile radar unit (1) positioned at the height of the crops in the plot, said radar unit being in communication with a processing unit configured to implement steps of:
- E1) transmission of frequency-modulated continuous waves towards the plot by means of the radar unit, the radar unit (1) illuminating a determined zone (z) of the plot;
- E2) obtaining at least one radar image (Ir) of the plot (20) cultivated by means of the radar unit (1), said image consisting of voxels or pixels each comprising a level quantifying a quantity of waves reflected by the crops (5) of the plot;
- E3) processing of the acquired image to obtain at least one parameter (e _av , N _e>eref ) indicative of the leaf area of the plot. Method according to claim 1, comprising a step E4) of moving the radar unit (1) within the plot so as to obtain images of the entire plot, the method comprising, for each position, radar unit (1) a step E5) of repeating steps E1) to E3). Method according to one of the preceding claims, in which the said at least one parameter indicative of the leaf area is:
- e _avg defines as being the average value of the levels of all the pixels/voxels of the image; and or
- N _e>eref defines as being the number of pixels/voxels for which the level is greater than e _ref ; Method according to one of the preceding claims, in which the radar image is multidimensional and comprises at least two of the following spatial dimensions: the depth of the area illuminated by the radar unit, the height of the illuminated area, the elevation, the width of the illuminated area and the azimuth. Radar image processing system comprising:
- a mobile radar unit (1) comprising a radar configured to acquire at least one image of the cultivated plot, said radar operating in the frequency modulated continuous wave domain;
- a processing unit (2) in connection with the radar unit and configured to implement steps of:
- E1) emission of frequency modulated continuous waves in the direction of the plot by means of the radar unit (1);
- E2) acquisition of at least one image of the cultivated plot by means of the radar unit, said image consisting of voxels or pixels each comprising a level quantifying a quantity of waves reflected by the crops of the plot
- E3) processing of the acquired image to obtain at least one parameter indicative of the leaf area of the plot. System according to the preceding claim, comprising a unit for moving the radar unit within the plot, the processing unit being further configured to control the movement E4) of the radar unit within the plot and to repeat for each position of the radar unit steps E1), E2) and E3). System according to one of Claims 5 to 6, in which the radar unit is configured to emit waves in a frequency band comprised between 24 and 125 GHz, preferably between 24 and 122 GHz, preferably at 24 GHz. Computer program product comprising code instructions for the execution of a method according to one of Claims 1 to 4, when the latter is executed by a processor.