Where to stand when measuring sunlight?

A user asked the following:

“I really like the app. So easy to use! 
“My latest use case is that I have 2 rows of 4 raised garden beds and the perimeter area is surrounded by trees. I want a reading for each bed. Where should I stand? Consistently at the head or foot of each bed? In the center of the bed (difficult as I currently have crops in them)? In the general vicinity of the 8 bed footprint ( 30×25 feet)?
“I’m taking readings for this area as well as each area I plan to grow in. I never know where to stand.”


As far as your use case, here’s the story.   SASHA measures the direct sunlight at the location of the camera.  If you stand at the end of a row, it will be measuring the sunlight at the end of the row at the elevation you are holding the camera.  Likewise at the middle of the row, etc.  Therefore, the most accurate measurement for the end of a row of radishes, for example, would be taken at the end of the row at the level (elevation) where the radish foliage will be.  Needless to say, it would be awkward to do that, although it is possible (e.g. lie down on the ground and take a measurement, or place a mirror on the ground to see the screen as you scan).   The only time I would recommend doing something like that would be when another low plant or obstruction is the cause of shade.   In most cases, where shade is caused by trees or buildings, standing at the location of interest, or a step or 2 South of the location, would be close enough.  You can use your own shadow a rough guide for how far away to stand.

Your growing plot is large enough that a “shade map” would be valuable.  A primitive shade map can made by subdividing your plot into squares (about a yard on a side) and taking a measurement for each each square.  Plot your readings on graph paper, or enter into a spreadsheet and create a “surface” plot.  It may not be practical to do right now, as you mention that your cops make it difficult to get into the middle of the beds.

Given that the crops are in the way and you can’t get into the middle of a bed, you might consider interpolation:  take a measurement at each end of the bed, and assume that the amount of light changes steadily (linearly) from one end to the other.   So if you have 4 hours on one end, and 8 hours on the other, you can assume that you have 6 hours in the middle of the bed.  This is an approximation, of course, but it might be better than nothing.  You can do the same thing across the beds….

Before you do all of this, make sure your device’s compass is behaving well.   The device compass is the largest source of inaccuracy in the app (due to the fact that the device itself creates electromagnetic field which can confuse its compass).  If you have a case with a magnet, take the phone out of its case. Do a google search for “Android compass calibration” and follow the instructions (usually some version of a figure 8).  A sure sign that the compass needs calibration is that the “tiles” (or “cells”) on your screen drift relative to the background scenery.   This drift means the compass has not “locked in” on North.

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