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Radiation Shield Comparison Lab

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About This MicroSim

Siting error is the highest-consequence and least-visible mistake a student station can make, because the data it produces looks entirely plausible.

Four sensors run through the same day against a known truth on one fixed axis:

  1. Bare sensor on a dark asphalt roof - reads wildly high, peaking in the early afternoon with the sun. It is measuring the roof, not the air.
  2. Bare sensor on a south-facing wall - reads high, and peaks later, because masonry stores heat all day and gives it back into the evening. The shape is the giveaway.
  3. Sensor under a simple sunshade, no airflow - much better, and still wrong. Shaded air with nowhere to go heats up and sits there.
  4. Sensor in a louvered white screen at 1.5 m over grass - tracks the truth all day.

Set the weather to Overcast and all four agree to within a fraction of a degree. That is the most important setting in the sim: on a cloudy day, bad siting is invisible. It is why siting errors go unnoticed for months. They only appear when the sun is out.

Diagnosis mode inverts the task. One curve, no label, and four buttons. Read the shape - when does the error peak, and how large is it? - and name the siting. Three rounds. This is the skill you will need in Chapter 15 when you are looking at your own suspicious data.

The physics here is a coefficient model, not real radiative transfer: solar load times an absorption factor times a shield factor, minus a ventilation term, with a per-siting time lag. It is tuned for the correct qualitative ordering and plausible magnitudes, not for numerical accuracy.

How to Use

  • Drag the Time slider through the day, or press Run the day and watch it play.
  • Read the panel: each sensor's current reading, its error against the truth, and its worst error so far. When the day finishes, the four are ranked.
  • Click a sensor name in the panel to hide its line and reduce clutter.
  • Change Weather to Clear and breezy and see which sensor benefits most. Then set it to Overcast and read the message.
  • Change Season to Winter. The errors shrink, but they do not vanish.
  • Press Diagnosis mode for three unlabelled rounds.

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Lesson Plan

Grade Level

6-12

Duration

25-30 minutes

Bloom's Taxonomy Level

Analyze (L4)

Prerequisites

  • Chapter 6 sections on what a thermometer actually measures
  • Reading a line chart against a reference line

Activities

  1. Watch the day (7 min): Clear and calm, summer. Run the day. Note the time at which each sensor reaches its worst error. Two of them peak at noticeably different times - which two, and why?
  2. Isolate the causes (9 min): Switch between Clear and calm and Clear and breezy. Which sensor improves most, and what does that tell you about what was wrong with it?
  3. Diagnose (10 min): Run all three rounds of diagnosis mode. For each, write down the clue in the shape that gave it away before you pressed a button.

Assessment

  • Attributes a specific error shape to a specific siting fault.
  • Distinguishes a radiation error from a ventilation error by how a breeze affects it.
  • Explains why a cloudy day hides a siting fault.

References

  1. WMO-No. 8, Guide to Instruments and Methods of Observation - the siting and exposure standards this lab is modelled on.
  2. NOAA National Weather Service: ASOS siting - how the professional networks handle the same problem.
  3. Wikipedia: Stevenson screen - the louvered white box, and why it is louvered.
  4. Wikipedia: Urban heat island - what happens when siting error is systematic across a whole network.