A virtual laboratory experience…….

The ITET “Rapisardi – Da Vinci” of Caltanissetta joined the European project S.T.E.L.L.E. proposed by PROTOM (see www.protom.com and https://business.esa.int/projects/stelle for futher informatin) as part of the recent “call for ideas” for the presentation of innovative proposals in the educational field. This project was selected by the E.S.A. (European Space Agency) which made its database and satellite images available.

Starting from this data and using the digital platform made available to the schools participating in the project, the students conducted a comparison activity between the data provided by the satellites regarding the average sea surface level and the emerged covered lands in the period between 1993 and 2015. This analysis clearly shows the criticality of the climate change process currently underway on our planet.

The students then deepened the study of the analysis methodologies conducted by the ESA using a virtual laboratory in which they measured the albedo of a scale reproduction of some terrestrial environments (arctic areas, cities, woods, coastal areas, etc.) and studied the correlation between albedo and the temperature of the Earth’s surface.

The work conducted by the students was presented on the occasion of the “STEM Discovery Campaign 2021” event organized on 30.03.2021 at the laboratory of the “Liceo Ilaria Alpi” school in Cesena (see the article: Laboratory simulation of the effects of climate change on Earth.) 

The global warming problem

Global warming is a complex phenomenon both in its form and in its understanding. It is linked to many causes and many are its consequences; for example, global warming is related to the greenhouse effect and the melting of the Earth’s ice caps is linked to the albedo of the planet, i.e. the Earth’s ability to reflect light. All unreflected light is absorbed by the Earth, contributing to warming. As the ice melts, which has a high albedo, its lowers the planet’s albedo, increasing warming.

Objectives of our students’ study were the:

● Understanding the effect of melting sea ice compared to the melting of glaciers and ice caps.

● Understanding the reflection of light according to the colour of the material.

In order to do it we used:

● Interactive thematic map – Land cover, Sea ice

● A laboratory experience – Albedo of different surfaces.

What is albedo?

The albedo (from the Latin albēdo, “whiteness”, from albus, “white”) of a surface is the fraction of light or, more generally, of incident solar radiation that is reflected in all directions. It therefore indicates the reflecting power of a surface. The exact value of the fraction depends, for the same material, on the wavelength of the radiation considered. If the word albedo is used without further specification, it is meant to refer to visible light. It is measured through an albedometer.

The maximum albedo is 1, when all incident light is reflected. The minimum albedo is 0, when no fraction of the light is reflected. In terms of visible light, the first case is that of a perfectly white object, the other of a perfectly black object. Intermediate values ​​mean intermediate situations. The albedo of fresh snow reaches up to 0.9. Coal has a very low albedo. A slate has an albedo of about 0.15. The albedo can also be measured as a percentage, setting 1 equal to 100%. The Earth has an average albedo of 0.37-0.39, or equivalently 37% -39%.

Albedo is an important concept in climatology, astronomy, and environmental management. The average albedo of the Earth from the upper atmosphere, its planetary albedo, is 30–35% because of cloud cover, but widely varies locally across the surface because of different geological and environmental features.

Earth’s surface albedo is regularly estimated via Earth observation satellite sensors instruments on board.

Earth’s average surface temperature due to its albedo and the greenhouse effect is currently about 15 °C. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below −40 °C. If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 °C. In contrast, if the entire Earth was covered by water – a so-called ocean planet – the average temperature on the planet would rise to almost 27 °C.

Relationship between albedo and temperature

The greater or lesser reflected incident radiation, and the consequent lower or greater absorption, respectively, can influence the temperature of a body. To give an example, the entire territory of the state of Belgium is considerably warmer than the open French countryside which lies immediately to the southwest, due to the effects of a different albedo.

The coldest regions of the Earth, rich in snow, having little light absorb due to the albedo of the snow, but the relationship between temperature and albedo is actually more evident in tropical regions, because the tropics receive a lot more sunlight.

This phenomenon is evident on a smaller scale. It is common experience that people who wear dark clothing in the summer often feel warmer than those who wear light-colored clothing.

Students calculated the albedo of different simulated enviroments in the virtual laboratory through the measurement of the radiant emittance.

The radiant emittance is the power emitted per unit area. In the case of thermal radiation, it is one of the components of the thermal flux, that is the radiant flux emitted by a non-point but extended source. In the International System of Units it is expressed in watts per square meter (W / m²). Satellite sensors use this physical parameter to calculate the albedo of the different parts of the Earth.

The STELLE project (STELLE – Satellite Technology to Enabling new Learning and Lessons Environment)

In order to better understand the climate phenomena related to the variation of the albedo of the earth’s surface, the students used the results provided by the European Space Agency (ESA) and their graphic representation within the platform created in the STELLE project, accessible through the link https://stelle.scuolabonline.com/login/index.php?id=1&code=Protom.

Thanks to this platform we were able to compare the situation of the surface of the seas and of the land emerged in the period of time between 1992 and 2015. The following images obtained from these analyzes show how actually the process of change of the Earth’s surface is proceeding to ever greater speeds.

Virtual laboratory experience: Reflection capacity of the ground and reflectance phenomena – Albedo of different surfaces 

The experience related to albedo, mainly an observation experience, is presented by the figure below. 

The experience aims to analyse how different materials have different optical properties, in particular how ice, water and soil have different albedoes.

In the virtual laboratory there are different sections of soil, with surfaces of different materials and colours.

A directional light source is simulated by the holographic generator, reflecting the characteristics of sunlight.

In addition, there is an albedometer designed to measure the intensity of the light source and the intensity of the reflected light. The data read by the sensor is displayed on the laboratory monitor.

With the measured light intensity data it is possible to calculate the albedo of particular surfaces.

By changing materials it is possible to experimentally verify that different materials have different Albedo values, marking each observation in the notebook.

By measuring the irradiation irradiated on the different surfaces and the reflected irradiation, the albedo of the different simulated environments was calculated through the ratio of the measured values. The results obtained are showed in the following table.