Re: [EE]:: Twilight Photometers - Forest Mims latest games

SOMETHING WORTH LOOKING AT JUST BECAUSE OF ITS ASTOUNDINGLY ELEGANT
SIMPLICITY AND EXTENSION OF MEASUREMENT ABILITY TO FAR BEYOND WHAT MAY BE
INTUITIVE.

I should have included an abstract. This is rather brilliant in its useful
simplicity.

As the sun sets a twilight shadow line sweeps across the sky and for a
given narrow-angle optical sensor pointing angle the altitude of the
sun/shadow boundary rises.
An "ordinary" LED and (here) a 25mm dia lens allow an eg 0.3 degree viewing
angle. The moving sunlit:shadow boundary scans the air column and
reflections (mainly) from aerosols, dust particles and allow the height of
the troposhere to be determined with reasonable accuracy (based on sounding
balloon results).
One of more LEDs are used as narrow bandwidth photo sensors with peak
spectral output at slightly below their emission frequency.

Excellent reference / overview:
https://journals.ametsoc.org/view/journals/bams/aop/BAMS-D-24-0054.1/BAMS-D-24-0054.1.pdf
____________

" Twilight photometry and its detection of the tropopause came of age in
1956, when E. K. Bigg used a searchlight mirror to focus twilight onto a
photomultiplier tube to measure the height of aerosol layers over central
Australia as the sun sank below the horizon (Bigg 1956). Bigg found a
significant 15 km aerosol spike on 2 November 1955 over central Australia. "

"In May 2022, an improved LED photometer amplifier was designed by Hagerup
Technical Services for a National Aeronautics and Space Administration
(NASA) project to measure the altitude of aerosols from the historic Hunga
Tonga eruption on 15 Jan 2022. The LED was installed at the focal point of
a 25-mm diameter lens installed in a 100-mm lens tube. This telescope has a
field-of-view (FOV) of 0.3 degree, slightly more than half the diameter of
the solar disk. The telescope significantly increases the twilight signal,
and the narrow FOV helps to eliminate the interference from stars." ...

 "The tropopause height has been measured by sounding balloons for more
than 70 years. More recently, lidar has found the tropopause height by
detecting aerosols or subvisible cirrus that accumulate at the tropopause.
Here we present a twilight photometer technique to detect the tropopause
height with results close to the traditional World Meteorological
Organization (WMO) method from sounding balloon measurements. The twilight
intensity (I), although radiometrically uncalibrated, can be normalized by
the derivative of log(I) with respect to time (t), or I’(t)/I(t), to infer
stratospheric aerosol layer properties using Earth’s shadow to orderly
shield the sunlight below different altitudes. A conventional twilight
photometer detects the twilight glow from atmospheric aerosol scattering
with a photodiode detector equipped with a near-infrared optical filter. We
have replaced the photodiode and optical filter with a LightEmitting Diode
(LED) that functions as a wavelength-dependent photodiode with a
narrow-band response near 1050 nm. We found that the layer height from
twilight photometer observations is highly correlated with the tropopause
height. 76 twilight tropopause heights during the first six months of 2024
at Geronimo Creek Atmospheric Monitoring Station (GCAMS) in Central Texas
agree well with those reported by sounding balloons launched from Corpus
Christi, Texas, 207 km from GCAMS (standard deviation of 265 m). The
twilight method is inexpensive, easily implemented, and has potential for
use at remote sites with solar power and developing countries that lack
resources for sounding balloons. It can also provide a learning tool for
students of meteorology and the atmospheric sciences."

____________________

On Wed, 7 Jan 2026 at 09:57, RussellMc <[email protected]> wrote:

>
> On Facebook group "I Take Pictures of Electronic Parts
> <https://www.facebook.com/groups/253864931469516/?__cft__[0]=AZb0tYaHl-o6byttQMVFXrtx7IvEQ3erBftsA8MgvQ8gdUL7LuvdYj_suAAog_HPEEfkxygxbIOD38-ohn6R0n0_U0c2aJoWHdwhrxWmDcqApQVtj8ivkUrYRfsmMOPhwEHitCMNn5_QQq67mohBQ20w&__tn__=-UC%2CP-R>"
> (recommended :-) )
>
> FM's post:
> https://www.facebook.com/groups/ElectronicParts/posts/2975756782613637
>
> FM's facebook page    https://www.facebook.com/forrest.mimsiii
>
> _____________
>
> Twilight Photometers
>
> Remarkably simple.
>
> https://makezine.com/projects/twilight-photometer
> <https://makezine.com/projects/twilight-photometer?fbclid=IwZXh0bgNhZW0CMTAAYnJpZBExV0Y2ZEdsOWhZOUxWYzJib3NydGMGYXBwX2lkEDIyMjAzOTE3ODgyMDA4OTIAAR5kWRrUbAbRpsQ1xIXDfdaTJ4IxW96oLTZBckTAJ_Vmnjt_hXlZRKKznN_jKg_aem_WMyau1ZoPRgBQr7E05FDGQ> -
> Forrest M. Mims III
>
> https://ntrs.nasa.gov/.../Twilight%20Near-Infrared...
> <https://ntrs.nasa.gov/api/citations/20250006477/downloads/Twilight%20Near-Infrared%20Radiometry.pdf?fbclid=IwZXh0bgNhZW0CMTAAYnJpZBExV0Y2ZEdsOWhZOUxWYzJib3NydGMGYXBwX2lkEDIyMjAzOTE3ODgyMDA4OTIAAR66SnMTwzYemGv9OtClHpc8BbWtqQSr5_7kCQ3SF4Ee21uF4-pBBU8FIvqEhQ_aem_Nrqqe1AVF5SeVRMQn2HN0Q> -
> co author
>
> https://www.mdpi.com/2072-4292/17/12/2071
> <https://www.mdpi.com/2072-4292/17/12/2071?fbclid=IwZXh0bgNhZW0CMTAAYnJpZBExV0Y2ZEdsOWhZOUxWYzJib3NydGMGYXBwX2lkEDIyMjAzOTE3ODgyMDA4OTIAAR7FiuwzFT6axggd8u8p6QR7fd2vvMhkINPTkK8B04nH4EGJfIHohY7F9Km4GA_aem_JwUOdMAnUAoXVhFTA_Qcfg>
>      https://www.mdpi.com/2072-4292/17/12/2071
> https://journals.ametsoc.org/.../BAM.../BAMS-D-24-0054.1.pdf
> <https://journals.ametsoc.org/view/journals/bams/aop/BAMS-D-24-0054.1/BAMS-D-24-0054.1.pdf?fbclid=IwZXh0bgNhZW0CMTAAYnJpZBExV0Y2ZEdsOWhZOUxWYzJib3NydGMGYXBwX2lkEDIyMjAzOTE3ODgyMDA4OTIAAR66SnMTwzYemGv9OtClHpc8BbWtqQSr5_7kCQ3SF4Ee21uF4-pBBU8FIvqEhQ_aem_Nrqqe1AVF5SeVRMQn2HN0Q>
>
>
>
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