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Calibration of a Skye Ltd. multispectral sensor (large tripod) using a reflectance panel (small tripod). Photo: Lars Eklundh. Calibration of a Skye Ltd. multispectral sensor (large tripod) using a reflectance panel (small tripod). Photo: Lars Eklundh.

The multispectral sensors used in SITES Spectral are regularly calibrated, to monitor their performance and detect possible misfunctioning. By training the personnel at each station, the time the sensors are not collecting data is reduced and the frequency of calibrations can be increased to once a year. Therefore, SITES recently organized a calibration workshop for personnel at the stations.

The workshop had several aims. First, to share knowledge among the stations and technical stuff and strengthen skills within SITES Spectral. Second, to improve the efficiency of data collection and quality. Last but not least, it is positive for the staff at the stations to have a comprehensive understanding of the entire data generating process.

During the workshop, there were discussions about the necessary equipment, the best time and place to perform the calibration, the calibration process itself, and report of results on a calibration certificate. It was an interactive conversation where all participants shared their knowledge and experience for creating the best conditions for reinforcing the fundamentals needed to perform the calibration at their station.

Text: Virginia Garcia.
 

The Workshop was held on 17 February 2021 and was run by Virginia Garcia, Research Engineer in SITES Spectral (virginia.garcia@nateko.lu.se). Given Covid-19 restrictions, the workshop was held online. Personnel from seven SITES stations participated.
Recently, information about the more intensively studied lakes, in Thematic Programs SITES AquaNet and SITES Water, was added to the SITES website. There are seven lakes, Almbergasjön, Bolmen, Erken, Erssjön, Feresjön, Stortjärn and Tarfalasjön, at seven different stations that are central for SITES AquaNet and SITES Water. Use the link below to read more about each lake.

The lakes in SITES AquaNet and SITES Water
 
View of the phenocameras and NDVI sensors placed in the tower and the calibration equipment. Photo: Ryan Davidson. View of the phenocameras and NDVI sensors placed in the tower and the calibration equipment. Photo: Ryan Davidson.

After a mild autumn, the real winter has arrived at Lönnstorp Research Station. Over the last two weeks, temperatures have been below zero, with a minimum of -12ºC, according to the automatic weather station. These low temperatures have caused ice to form on the sea surface, which is just 3 km away from the station, and the fields around the station are covered in snow.

Despite the winter conditions, the station staff are already thinking about the spring season, as there is less than two months until the first crops should be sown and therefore time to check and calibrate the spectral equipment.

Solar panels that supply energy to the tower equipment. Photo: Ryan Davidson.
Solar panels that supply energy to the tower equipment. Photo: Ryan Davidson.
The spectral equipment consists of three phenocameras and two NDVI sensors (see fact box), powered by a solar panel and placed on a 10 meter high tower. The station staff implement regular revisions of all equipment and currently they are calibrating the NDVI sensors.

Text: Ana Barreiro.
 

Normalized difference vegetation index
Normalized difference vegetation index (NDVI) is an index that describes the greenness of the vegetation. Through SITES Spectral, SITES monitors NDVI at Lönnstorp Research Station and six other stations.

The data from SITES Spectral is available through SITES Data Portal.

Climbing to reach the soil sampling site 17 June 2014. Photo: Therese Zetterberg, SLU. Climbing to reach the soil sampling site 17 June 2014. Photo: Therese Zetterberg, SLU.
Studying natural or semi-natural forests gives us a better understanding of the effects of forestry. However, since disturbances such as storms are a part of natural ecosystem, field work is sometimes challenging.

The monitoring program IM - Integrated monitoring - follows both physical and chemical processes and their impact on the biological system in four small catchments dominated by coniferous forest, located in different parts of Sweden’s climate and air pollution gradients. One of the areas, Aneboda IM, is through SITES associated with Asa Research Station. A severe storm hit Aneboda sixteen years ago, and the effects are still impacting the biogeochemical status and field work in the area.
During 8–9 January 2005, southern Sweden was hit by Cyclone Gudrun. At Aneboda IM, maximum wind speeds exceeding 20 meters per second were recorded over nine hours. About 15–20 percent of the trees were knocked down by the storm.

After the storm, the fallen Norway spruce trees (Picea abies) attracted bark beetles (Ips typographus), which caused a massive insect outbreak. The beetles infested a large proportion of the Norway spruce trees that survived the storm. In the 2011 survey, almost half of all Norway spruce trees with diameters larger than 20 cm were dead.
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The slideshow above shows how the forest in one of the plots where the vegetion is monitored changed from a closed old growth Norway spruce stand to an open area with primarily birch saplings and large amounts of coarse woody debris, during the years 2004–2019.
These change benefits the biological diversity in the area, but it makes part of the monitoring more difficult. As the pictures above and to the left show, both vegetation and soil sampling surveys have become a challenge for the field staff.

Text: Stefan Löfgren and Ulf Grandin, SLU.
Facts about Aneboda IM
The Aneboda IM site and the nearby forest and bog are part of a nature reserve. Long-term monitoring in Aneboda IM was initiated in the mid-1990s in semi-natural coniferous forests, where atmospheric deposition of pollutants and anthropogenically induced climate change are the main human disturbances.
Aneboda IM is one of four Swedish IM catchments within the program Long-Term Ecosystem Research in Europe (eLTER). These programs provide infrastructure, data and management for research at reference conditions on hydrological and biogeochemical processes, including interactions with the biota.
 
Issues of special interest are soil and surface water acidification, weathering, carbon sequestration, leaching of nutrients, DOC and trace metals, including Hg, as well as the biological effects on organic matter decomposition, bioelement uptake by vegetation and changes in the microbial and vegetation communities down to species level. The semi-natural state at these sites defines the limits for what could be expected without forest management, e.g. defining background conditions and elemental dynamics at reference conditions.
Röbäcksdalen’s 75 cm record snow depth, with the field station building in the background. Photo: Malin Barrlund. Röbäcksdalen’s 75 cm record snow depth, with the field station building in the background. Photo: Malin Barrlund.
The weather this winter around Umeå in northern Sweden has so far been erratic. Both November and December were unusually warm with little snow, but in January the temperature fell, it started to snow, and multiple snowstorms occurred during a period of just a few days.

Snow situation at Röbäcksdalen
Röbäcksdalen Field Research Station is measuring snow depth since 2010. So far this season, 75 cm of snow have accumulated at the station, which is the deepest snow cover since the recording started. Usually, the highest snow depths are measured later in the season which shows the magnitude of the current situation and that there is a possibility for more snow to come before this winter is over.
Almost a meter of snow at Svartberget – a record for January
At Svartberget research station, about an hour drive inland from Umeå, the snow depth increased with over 60 cm during the period with several snowstorms in January, which added onto the already existing snow cover.
Digging out field equipment (this one is measuring ozone) is a big challenge this year at Svartberget. Photo: Pernilla Löfvenius.
Digging out field equipment (this one is measuring ozone) is a big challenge this year at Svartberget. Photo: Pernilla Löfvenius.
Svartberget has measured snow depth since 1980 and the record so far is from 1988 when 113 cm was recorded. A lot of the snow that year fell in February and March. The accumulated 97 cm of snow this January is the deepest ever recorded so early in the season, but the most astonishing is in how short time the snow assembled.

The local newspaper refers to old farmer’s traditions, which says that half of winter’s snow should have arrived by now. However, data from previous years at Svartberget show that half the amount of snow usually has arrived by Christmas time and that the maximum snow depth is in the beginning of March. The same data supports the likelihood that another 10-20 cm of snow will fall before the winter is over. However, the variation between years is large and climate change makes it difficult to predict the weather, especially in the past years.
Snow depth (cm) over a season at Svartberget. The red line shows this season. The dashed line is the the minimum, the black line is the average and the dotted line the maximum for the period 1980-2010.
Snow depth (cm) over a season at Svartberget. The red line shows this season. The dashed line is the the minimum, the black line is the average and the dotted line the maximum for the period 1980-2010.
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