Crop Water Stress Sensor

This sensor measures crop water stress using a thermal camera and communicates drought inflicted crop damage to farmers and a wider public.

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The Crop Water Stress Sensor measures and visualizes the drought stress that usually affects plants during a dry period and logs the results to an SD card.

Due to climate change, droughts and dry periods will become more frequent. The consequences of a drought are often a reduction or failure of the yield and a general decrease of the yield quality. Because our food supply crucially depends on good harvests, it is high time to make people aware of the problem, collect data and develop more resilient agricultural systems.

The Crop Water Stress Sensor is designed to intuitively show the often non-obvious water stress of our crops while collecting valuable time series data on an SD card. The device will be supplied with LoRaWAN in the next version to be able to send the data also to sensor networks.

The sensor is very useful to farmers, scientists and communities to asses the water stress status of crops and plants ans supports the concept of climate resilient agriculture.

The challenge:

Due to climate change, droughts and dry periods have become more frequent with an increasing trend in the future. This lack of water usually has a negative impact on crops and thus our food supply and  our food security. In particular, regions that previously had no serious water problems will be affected by droughts in the near future, including the main growing areas of our staple foods. The consequences of a drought are often a reduction or failure of the harvest and a general decrease of the harvest quality. However, apart from a few side notes in the news, the drought induced problems of crop cultivation and the threat to our food supply are not a major concern for most people and communities.

With this project, I wanted to make the water stress of crops visible to a wider range of people and raise awareness of how directly weather extremes such as droughts are related to our food and how big the problems for agriculture can become due to prolonged dry periods.

It is therefore high time to make people aware of the problem, collect data and develop better more climate change resilient agricultural systems.

The Crop Water Stress Sensor:

The Crop Water Stress Sensor is designed to intuitively show the often non-obvious water stress of our crops while collecting valuable time series data on an SD card. Using a low-cost thermal imaging camera (MLX90640), plant surface temperatures are recorded and the Crop Water Stress Index (CWSI) is applied using these data. The CWSI is the standard remote sensing method to calculate crop water stress e.g. from thermal satellite imagery and this index is ideal to apply with the data from the small thermal camera. The results of the CWSI are shown on the display (ILI9341 3.2") as current measurement, daily average, 14-day retrospective and 5-day trend (see below).

In the picture above you can see what the dashboard on the display looks like. The top section displays the current daily average of the crop water stress index and the last reading with the latest time stamp. I also thought it would be nice to display the timestamp of the first row of data that was logged on the SD card. The main figure of the dashboard shows the daily mean crop water stress values of the past 14 days. The background colors also indicate the severeness of the crop stress and are intended to be a visual aid. Since I didn't have the time to run the sensor for two weeks in the field yet, only the last 7 days and the current average are displayed on the screen so far.

Working in crop and climate science, people often tend to see me as a weatherman for crop performance predictions and one of their first questions is usually if I can predict how the crop is going to perform in the future. Since I also don't have crystal ball, I usually refer to a trend estimate based on a regression. To keep things simple here, I implemented a linear regression for the last five days of measurement and the resulting slope is then interpreted as the trend. There is a plethora of statistical procedures that I could use as alternatives here and maybe I'll change the procedure in the coming versions.

Finally there is still a big black spot that is not used on the display on the right bottom corner. I plan to integrate a watering suggestion here to give more practically usable advice to the people who look at this dashboard. I didn't have the time to implement any of this yet, but it could look like one of these suggestions:

During midday hours, the display is a little hard to read, since the sun light is usually very strong. I'm currently experimenting with other display types (such as E-ink) and anti-reflection films to see if I can improve the visibility of the prototype. However, the simplest solution to display the CWSI results during the sunniest hours of the day would be a simple "traffic light" style based on cheap Neo-pixels. Here, green light indicates no or low drought stress, orange...

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  • 1 × MLX90640 IR Thermal Camera Breakout (75€)
  • 1 × ESP32 NodeMCU Dev Kit (9€)
  • 1 × DS1307 real time clock with battery (4€)
  • 4 × WS2912b neo pixels (2€)
  • 1 × perforated grid board (1€)

View all 24 components

View all 11 project logs

  • 1
    Building the Crop Water Stress Sensor

    Like for most builds, these instructions start with the suggestion to fire up your 3D-printer and to start printing the 3D objects. I can recommend to use material that will last long outdoors and doesn't degrade with the weather conditions such as PETG or ASA filaments. On a regular 3D printer this will take around 2-3 days of printing time:

    For the solar panel mount there is also one .svg file for a laser cutter. If you don't have access to a laser cutter, a good old fretsaw will also do the job.

  • 2
    The sensor box central component setup

    Let's start with the insides of the sensor box:

    Screw the 8 6mm screws into the support frame:

    Then add 6 regular 5mm spacers and two with the screw end to the other side of the support frame:

    Add the solar power management unit to the left side of the supply frame. Use 4 of the 15mm spacers (always two on top of each other) for the left side and two 6mm screws to fixate the right side:

    Now ideally we would use a PCB board for the next step, however I wanted to show that we can also just use good old fashioned perforated grid board here. Please note that the pin sockets for the display are elevated by 30mm to receive the display without the necessity of a cable (central picture):

    Now we can also screw the second board into place using 4 15mm spacers and 2 nuts that are not displayed in the picture here for the right side:

    Now we can add the ESP32 board that should just slide smoothly into place:

    Then we can prepare the cover piece, adding the Neo-pixel strip and the real time clock. I used hot glue, you can of course also use tape or screws:

    Connect both components with wires to the main board:

    We further add a power supply wire between the solar power management board and the main board, and also add the cables for the SD-card slot on the display board:

    Finally the display pins are connected to the elevated receivers. If these receivers are exactly 30 mm in height, the display will be easy to connect. Note that this is just a suggestion to avoid the necessity to use a very short cable to connect the screen:

    The display can then be mounted on the assembly:

    For the next step, I forgot to take enough pictures, so here is a small summary: I use a 158x90x60 mm water proof, semi-transparent box to house the battery and the main interiors of the sensor system. We have two cables connecting the box with the thermal camera and the solar panel. These cables have to enter the box on the lower side. To make this water tight and dust resistant, I used two cable glands to seal the cable entries to the box against humidity. For these cable glands, two holes have to be drilled into the box.

    When both holes are drilled, the cable glands are inserted loosely and the attachment X is added to the backside of the sensor box. I used Torx-screws, however, any screw should be fine here. In the picture below, you can see the setup with both cables already in place.

    Now we can add the cables for the solar panel and the thermal camera through the cable glands, as you can see in the picture below. Note that I added a connector to the camera cable so that it can be easily connected to the main board via the pins. Further I use double sided tape to glue the battery in place.

    With the battery installed, it is now time to add the main box component that we assembled before. First I connect the solar panel cables and the battery cable to the power management unit. Then, I use four Torx-screws to attach it to the box. After the main component is screwed in place, it is time to connect the thermal camera cable to the main board.

    So far the screen is only attached via the pin connectors. In a next step, the cover plate that was resting above the box in the picture above is screwed in place connecting the screen firmly with the main box setup. This process is a bit fiddly, since the plastic screws and the 3D-printed holes are not perfectly round. I think you can save quite some effort here when using brass spacers and steel screws for the project.

    As you can see in the picture above, this should nicely fit into the sensor box and cover up the entire interiors of the sensor. This is now the best time to add an SD-card to the SD-card slot.

    Finally the box can be closed carefully using four screws and the sensor box setup is ready.

  • 3
    The thermal camera

    The thermal camera is the actual sensor of this sensor system. For this prototype the camera case was 3D-printed in white and covered with several layers of clear coat. However, for my tests, it was very dry outside and this setup might not survive several month outside with strong rains and intense sunlight. I'm seeking to improve this in future versions.

    The thermal camera is connected to the four wires of the cable leading to the main sensor box. Then the two pieces of the camera box are glued in place. I sealed them with clear coat too. However, this camera box needs quite a bit of improvement in the future. I thought about using a professional camera case and remove the front cover glass (since the thermal camera cannot be covered by glass). The camera is then attached to the camera shield using four Torx-screws.

    The final camera setup should look like this. I use a 45° angle to position the camera and a black plastic coated screw to adjust this angle.

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