Measurements Flashcards
Why is the biosphere difficult to measure?
The biosphere’s actors span a huge spectrum in space scales (orders of magnitude).
Why is the biosphere difficult to study?
- We only have one replicate.
- We cannot manipulate the biosphere and compare it with an unaltered control.
- The record is complicated by the super-positioning of many processes that are correlated with one another and operate across a spectrum of fast to slow time scales.
What is a pool?
Volume; content
What is a flux, and why do we care?
A flux is the action or process of flowing or flowing out. We care, because when we study systems of the biosphere, we are concerned with flows of material and energy.
What is homeostasis?
The tendency toward relatively stable equilibrium between interdependent elements, especially as maintained by physiological processes.
When do we use the top-down approach to study the biosphere?
For large complex systems, such as measuring the absorption of sunlight and relating that to growth
What is the bottom-up method?
The bottom-up method breaks the system into its constituent parts, tries to measure or model each component, then add them up. For example, if we were to use this method to estimate our class’ metabolism, we would select a sample of students, collect their metabolic rates and use that information to guesstimate the metabolism of the whole class.
Why is the bottom-up method less accurate?
We often don’t know enough about the model parameters, and there can be surprises like scale emergent properties.
Tell me about global circulation inversion models.
Global circulation inversion models deduce sources and sinks of trace gas concentrations across the globe and wind fields. It divides the Earth into grids. These models allow us to map sources and sinks based on the transport field information provided.
Tell me about remote sensing.
Remote sensing measures reflected light and provides information on fluxes and vegetation status. Using this method to gain insight about vegetation, for example, can tell us where vegetation is more and least concentrated, how much vegetation there is, and how may this vary over the course of a season. All of this information is deduced.
It provides us wall-to-wall information at a variety of scales, provides information at hard to reach locations and allows us to see the reflectance of light from different wavelengths. However, its information is largely inferential and suffers from the presence of clouds.
Tell me about eddy covariance technique.
Eddy covariance measures net flux by analyzing high-frequency vertical velocity (wind) and scalar atmospheric data. It samples up to 10 times per second, constructing means and fluctuations of means over a half an hour and computing the covariance between fluctuations.
It can determine exchange rates of trace gases over natural ecosystems and agricultural fields and is frequently used to estimate momentum, heat, water vapor, carbon dioxide and methane fluxes.
It is one of the few methods that measure fluxes directly, not inferentially.
Short: Allows us to measure fluxes over fields and ecosystems. Works on an hour by hour basis. Gives us representative fluxes of a type of ecosystem, but does not provide much information geographically.
What are the pros of eddy covariance?
- Direct measurement
- Minimal intrusion
- Evaluates fluxes on different time scales over a wide area
- Provides process information
What are the cons of eddy covariance?
- Nighttime biases when turbulence is weak
- Results don’t apply in complex terrain
What are cuvettes used for?
Measures fluxes regarding the study of small plots of soil or individual leaves.
What are the pros of using cuvettes?
- Direct measurement
- Can control leaf environment to assess response functions
What are the cons of using cuvettes?
- Modifies local environment, which disturbs flux
- Difficult to sample natural variation
- Small sample area
- Cannot work well over whole ecosystems
How can static chambers deduce fluxes?
By knowing how the concentration of a gas that is either accumulating or being depleted in the chamber varies in time.
What happens if there is a feedback between the source and sink and the concentration in the chamber?
It may bias the flux.
