# Principles of Energy Balance in Environmental Systems Lectures

Energy Balance principles are critical to understanding how radiation from the sun causes evaporation of water from: the ocean, the ground, and crop plants. Our crops are in the hot sun all day and use a lot of water to stay cool. There is no easy way to measure the amount of water they need, but we can calculate it using energy balance principles.

In this seven-lecture series, Dr. Bruce Bugbee, a Professor of Crop Physiology at Utah State University, explains the principles of energy balance in environmental systems. These principles, based on the first law of thermodynamics, are a corner stone in the larger discipline of Environmental Biophysics.

**Lecture Series Introduction**

**Lecture 1**

Outline - Lecture 1 Handout

- Introduction: The magnitude of water use in agriculture
- The challenge of measuring water use and evapotranspiration
- Reference books on environmental physics
- First law of thermodynamics: energy in equals energy out
- The seven components of the energy balance equation
- The magnitude of latent heat of evaporation
- Understanding energy and power
- Shortwave and longwave radiation
- E = mc
^{2}homework

**Lecture 2**

Outline - Lecture 2 Handout

- Key for homework: units conversion Calories v. calories
- Calculating the efficiency of photosynthesis
- Calculating absorbed shortwave radiation – importance of albedo
- The three components of shortwave radiation
- Definitions of shortwave and longwave radiation
- The Stefan-Boltzman Law for longwave radiation

**Lecture 3**

Outline - Lecture 3 Handout

- The concept of emissivity
- Calculating long wave emitted
- Calculating net long wave radiation
- Calculating net absorbed short and longwave radiation

**Lecture 4**

Outline - Lecture 4 Handout

- Understanding the radiation balance on Earth
- Differential absorption of shortwave radiation
- Reflectance of longwave radiation
- Wein's Law
- Planck's Equation

**Lecture 5**

Outline - Lecture 5 Handout

- Transpiration
- Absolute and relative humidity
- flux = driving gradient x conductance
- Calculating the driving gradient
- Determining stomatal conductance
- Modelling transpiration

**Lecture 6**

Outline - Lecture 6 Handout

- Conduction and convection
- Calculating boundary layer conductance
- Measurement of the driving gradient
- Modelling convective heat transfer

**Lecture 7**

Outline - Lecture 7 Handout

- Energy balance principles at night: Radiation frost
- Energy balance principles in the Penman-Monteith equation
- The Simplicity of Hagraves equation

Have questions about the lectures? Email us at techsupport@apogeeinstruments.com.