Plants from Space

Collecting field data to measure plants from space

Climbing towers in Finland, the Netherlands, and recently in Ghana, PhD candidate Amie Corbin is crossing borders to collect essential data on vegetation for the MULTIPLY platform. For her research at the Institute of Environmental Sciences at Leiden University, she studies the ecologically important plant traits that can be measured from space.

In order to model data and create earth observation products with the MULTIPLY platform, prior knowledge on the vegetational variables is needed. Corbin collects this knowledge. “I focus on variables that can be both physically observed from space and are ecologically relevant. These variables can be indicators for vegetation health, like chlorophyll and leaf water content.”

Most measurements of plant traits that are currently available are from the peak moment of its growing season. Corbin tries to fill in the knowledge gaps. “By measuring traits of plants at different moments of the year I try to get a grip on year-round phenology,” Corbin explains. “This gives us a better understanding of whether some characteristics are trade-offs or if they are consistent throughout the year.”

Challenges in the field
Corbin collects measurements from three different types of vegetation: mixed forest in Finland, coniferous forest in the Netherlands and tropical forest in Ghana. “We try to discover how different characteristics from plants are related to each other and how this relationship changes over time, at different latitudes.”Sprectrometer 1

Using a field spectrometer, Corbin measures the reflectance of light. This is similar to how satellites measure reflected radiation from space. But the field measurements result in a higher resolution. “To measure the reflectance, one sensor was placed at the top and one at the bottom. The more plants there are, the less of the light that can be used for photosynthesis will make it to the ground level. Based on this difference we can measure the Leaf Area Index, the amount of leaf area,” Corbin explains.

Tower 1Collecting the measurements and samples was challenging. “The observation tower that we had to climb to take the samples and collect measurements was quite high, around 30 meters. I was a bit scared to climb the tower and enter the platform at the top, which was quite small,” Corbin admits. Fortunately, she was accompanied by a local guide and an expert tree climber who helped her out. “Our hosts in Ghana from the Forestry Research Institute of Ghana were great.”

Tower 2

The fieldwork was done every two weeks at the same location. “Because the sampling is destructive, and two weeks is enough to let the plants live,” Corbin explains. “Also, it is a lot of samples to process each time.”


Convenient collaborations
A big challenge Corbin encounters during her research is the clouds. Because clouds influence her imagery. “As a person who does not like the heat I am glad when a cloud shows up but as a scientist I really need them to be gone,” says Corbin. Fortunately for her, there are other researchers in the MULTIPLY team who atmospherically correct the images.

Corbin is enthusiastic about the collaborations within the MULTIPLY project and the platform that is being built. “I like that we collaborate not only with other universities but also with big companies. This is really helpful in creating an easy to use platform for remote sensing imagery.”

Review Meeting at Tartu Observatory

At certain points during a Horizon 2020 Research & Innovation Action, the project consortium meets for a review meeting. Together with the project officer of the European Commission and with an external reviewer they review the progress of the project. For the MULTIPLY project, on the 28th and 29th of Augustus, one of these review meetings took place at the Tartu Observatory in Estonia.

“It was a really nice and constructive meeting where we could present the current state of the project to the reviewers,” says Dr. Lea Hallik, team member of MULTIPLY and researcher at the University of Tartu. “As we are now finalizing the tests of the beta version of the platform, they were happy with our progress.”

Different types of users
“An interesting discussion was about how the platform should be accessible for two types of users. On the one hand, the more technical programmer that wants to create and improve products using satellite data. On the other hand, the earth observations consultants who are less technical and want to access only the end products. This is challenging and something we will have to work on during the next months.”

There was also time for some social activities like a nice tour along the visitor center and the space technology laboratory. “The location was great. It is in a beautiful green setting, 20 kilometers away from the city Tartu and its light pollution.”

MULTIPLY consortium members at the Tartu Observatory

MULTIPLY consortium members at the Tartu Observatory

From local to global
Hallik and her colleagues from Tartu University, study what kind of plant traits can be measured with satellites. Therefore, she collected data in the field on traits of both evergreen and deciduous trees during the past two summers. With this knowledge, she can validate the measurements from satellites. “I like that we, as a small research group, can contribute with local field measurements to such a big project.”

“In Estonia, we have six towers where you can reach the highest leaves of the trees. There we sample and measure leaf traits like reflectance, transmittance, pigment content, dry mass area, and water content. Because natural vegetation is very complex, especially in a forest, with multiple species and different vegetational layers, satellite data can also be challenging,” Hallik explains. “It is important to understand these time series of forest leaves because an important aim of MULTIPLY is to create time series and make seasonal changes visible.”


Samling at Järvselja forest, Estonia

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Observation tower at Järvselja forest, Estonia

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Fieldwork at Järvselja forest, Estonia

Fieldwork in Ghana

Amie Corbin is a PhD student at img_20180607_094410Leiden University who develops vegetation priors for the platform. From June to Augustus she will be in the Kogyae Strict Nature Reserve in Ghana to collect data. You can follow her adventures through her website.



Fieldcampaigns Land Cover and Soil Types

A comprehensive field campaign is conducted by the Ludwig-Maximilians-UniversitP1000160ät München (LMU) to collect in situ information for the validation of satellite-based retrievals of land surface parameters. These measurements will be used within MULTIPLY to validate the retrieval results of the MULTIPLY platform.
“Our campaign will last for the entire vegetation period in 2017 and collects data from a variety of different land cover types and different soil conditions”, says MULTIPLY team member Prof.dr. Alexander Loew.


During the LMU campaign essential characteristics of vegetation and plant conditions are collected, like e.g. information about vegetation biomass and water content as well as the soil moisture content. In addition, ground-based measurements of the surface radiation fluxes and spectral properties of the plants are collected. The LMU team goes into the field on a regular basis during COPERNICUS SENTINEL satellite overpasses.