Remote Sensing and Crop Phenology
What is remote sensing?
Remote sensing can have many different definitions, one popular definition mentioned in Thomas M. Lillesand's book Remote Sensing and Image Interpretation goes as follows:
"Remote sensing is the science and art of obtaining information about an object, area, or phenomenon through the analysis of data acquired by a device that is not in contact with the object, area, or phenomenon under investigation."
How are data acquired?
When energy sources propagate energy through different medias, these energies come in the form of electromagnetic waves. These electromagnetic waves come in different wavelengths and can be received by various types of sensors.
What are the sensors we use everyday?
Our human eyes! Although human eyes can only observe a very narrow range of EM waves (the visible range in the graph), they are still brilliant EM wave sensors!
How do sensors work?
Different sensors are designed to receive electromagnetic waves with different wavelengths. Think of the electromagnetic waves as keys and the sensors as keyholes, in order to properly fit the keys, the keyholes must be made to have the right sizes. So are the electromagnetic waves and their sensors!
Satellite imagery is one of the most common types of remote sensing data!
The picture on the left is a satellite image taken by the PlanetScope satellite. It is showing two towns called Urbana and Champaign, where the University of Illinois at Urbana Champaign is located at.
What happened to the color at the top of the picture? Why is it slightly darker?
The image on the left is not a single image, but two images stitched together! Satellites cannot take images of the whole earth at once. Instead, satellite cameras normally take pictures strip by strip, and each strip will cover certain amount areas. You can think of the satellite as a brush, and the earth as a wall, since your brush is not big enough to paint all the wall at once, then your only choice is to go strip by strip!
What are other types remote sensing?
The graph below shows some common sensors and the images produced by these sensors. These sensors can receive much broader ranges of EM waves.
Top row: 1. Digital Camera 2. LiDar 3. Drone 4. Digital Camera 5. Satellite; Bottom row: A. PhenoCam Image B. LiDar Image C. Aerial Photo D. Camera Image E. Satellite Image
What is Phenology?
The textbook definition of phenology goes as: "Phenology is the study of timing of biological events and their relationship to seasonal climatic changes" -US/IBP Phenology Committee (1972)
You can think of phenology as the color change of the plants. Take a look at the graph below which is showing the color change of soybeans from July to November.
The growing cycle of soybeans. The pictures were taken in July (upper left), August (upper right), September(lower right), and November(lower left)
Why study crop phenology?
Monitoring crop phenology has many implications: things like understanding the growing cycle of the crops, predicting the yield of the crops over large areas
What information we can get from studying Phenology?
We can get key phenological stages of the crops through studying crop phenology
How does remote sensing improve the efficiency of studying phenology?
Traditional phenology studies rely on field observation, however, the involvement of remote sensing can observe the phenology of crops in large areas and thus making the observation more efficient
