Field Exercise #3

 

Measuring the Net Radiation in

Diverse Environmental Systems

 

 

 

Introduction:

 

          In this week’s field exercise we will be returning to Nottingham County Park to measure the net radiation at several different sites.  The net radiation is an extremely important atmospheric variable because the net radiation at the earth’s surface provides the energy needed for processes such as warming the earth’s surface, evaporation, plant transpiration, diverse chemical and biological processes, etc. 

 

          All objects (that have temperatures above absolute zero; 0 K) emit radiation of some type.  ALL OBJECTS including you, your classmates, the computer screen that you’re looking at right now, EVERYTHING. 

 

 

The character of radiation that is emitted by an object is dependent upon the temperature of the object.  Two very important formulae relate the temperature of an object to the amount and wavelength of the radiation that is emitted by the object. 

 

                   Steffan-Boltzman Law:     E = sT4

 

                   Wien’s Displacement Law:         l = C / T (K)

 

 

          To measure the net radiation we will need to measure two types of radiation common to the earth system; shortwave and longwave radiation. 

 

Shortwave radiation is the type of radiation that comes from the sun.  This radiation is commonly assumed to have a wavelength (l) of between 0.2 mm to 2.0 mm (visible light has wavelengths of between 0.4 mm to 0.7 mm).

 

Longwave radiation is the radiation that comes from the majority of objects at the earth’s surface (soil, plants, animals, humans, rock, water, etc.).  The earth’s atmosphere also gives off longwave radiation. This radiation is typically assumed to have a wavelength of between 2.0 mm to 40 mm (most objects, including humans give off radiation at about 10 mm).

 

 

          To measure the shortwave radiation we will be using an instrument called a pyranometer.  We will need to measure the shortwave radiation coming toward the earth’s surface (incoming shortwave radiation) and the shortwave radiation that is reflected by the earth’s surface (outgoing shortwave radiation).  Thus, we will be using two pyranometers, one facing upward (measuring incoming shortwave radiation) and one facing downward (measuring outgoing shortwave radiation).

 

          To measure longwave radiation we will be using a different instrument called an infrared temperature gun.  Once again, we will need to measure the radiation moving from the earth toward the atmosphere (outgoing longwave radiation) and from the atmosphere toward the earth (incoming longwave radiation). 

 

         

 

The Laboratory Exercise

 

 

We will be measuring the net radiation at three locations within Nottingham Park.  These locations include a deciduous forest environment, a “savannah location” and a landscape cleared by humans.  At each station we will take measurements of the following radiation variables every minute for a 15-minute period:

 

 

1)       Rsd - using pyranometer #1

 

2)       Rsu - using pyranometer #2

 

4)       “sky” IR temperature using the IR temperature “gun”

 

5)       surface IR temperature using the IR temperature “gun”

 

6)       the time of the observations (approximate)

 

7)       sky conditions

 

8)       the percentage of the sky hemisphere obstructed (estimate)

 

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**      Please calculate the albedo (A), using Rsd and Rsu

 

 

**      Please calculate the net radiation from the equation:

 

Rn = (1-A)Rsd + Rld - Rlu

 

**      Please compare and contrast the calculated and measured net radiation values at each site.

 

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Radiation Measurements Site #1

 

Sky Condition____________                                            Sky Obstructed________

 

 

 

Ob #            Time

 

SWR Down

 

SWR Up

 

Sky

Temp

 

Ground Temp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Radiation Measurements Site #2

 

Sky Condition____________                                            Sky Obstructed________

 

 

 

Ob #            Time

 

SWR Down

 

SWR Up

 

Air Temp

 

Ground Temp

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Radiation Measurements Site #3

 

Sky Condition____________                                            Sky Obstructed________

 

 

 

Ob #            Time

 

SWR Down

 

SWR Up

 

Air Temp

 

Ground Temp