Hi,
We are trying to generate chart-based cone-catch method using pastel (48 colors). We found detail steps in this and this pages. We understand that these steps should be done under a sunny day as fast as possible. Yet there are still somewhere confusing. (Ocean Optic spectrometer was used.)
Based on Jolyon’s reply in 2021
1. “Set the spectrometer white point using the white standard, and it’s black point as you usually would.”
>> We are confused about “it’s black point as you usually would.” We usually adopt spectrometer in dark room, using light source from itself. When measuring outdoor, does that mean we should measure two grey standards (e.g., white: 99% and dark: 2%) under the sun light? Or measure the white point under sun light, but black point without any light, such as blocking lights from the probe? Should we turn on the spectral meter light source (I guess not, but check with you again)?
2. “Always measure surfaces from e.g. 45-90 degrees from the surface (vertical/elevation) and ~80 degrees (horizontally/azimuth) relative to the sun.”
>> We understand the purpose of this step, yet this post said “light source coming in from an angle, and spec and camera measuring from directly above.” It sounds like we should measure pastel vertically (90 degree). My first question is, suppose we are measuring under the sunlight at noon, I guess we should put the probe with some angle? Second, I am afraid misunderstanding what you mean about “~80 degrees (horizontally/azimuth) relative to the sun.” So, I attached a schema here, it will be very great if you could take a look.
3. “Measure the reflectance of one row of standards as fast as possible. At the end of the row, measure the white standard and black point again to check there has been no loss of either white or black point. If it doesn’t look perfect repeat the row again. Carry on working through the chart row-by-row, test-measure-test. Be aware that the sun is constantly moving (and the atmosphere slightly altering the lighting), so assume the calibration only holds for a few seconds.”
>> If the calibration only holds for a few seconds, shall we recalibrate spectrometer frequently? If yes, I wonder if different rows of pastel will be measured with different standards? Or the calibration standardizing spectrometer sensitivity to fit different light conditions? If not, in your experience, how long will be tolerable to finish all measurements?
This is our first time adopt spectrometer outdoor, so things are new to us. Thanks for kindly help!
Best,
Yung Chi