Mapping local skyglow sources

[discardedastro]

Where I live I have pretty low light pollution - I've got bortle 4 skies, by the maps, though I've never gotten a SQM and measured it.

However there's a few nearby industrial locations which I think are keeping their lights on all night and which I think are the source of quite a bit of the local skyglow; I'm keen to engage with them to ask them to cut back and switch to eco-friendly lighting with better control and/or switch their lights off overnight.

Obviously one can hop in the car at midnight and go look to see which places are staying lit up all night but I'd like to be a bit more empirical and scientific about it, if nothing else to evidence my requests and provide a basis for comparison should I be successful. I did a project a couple of years back for my company using laser mapping with GPS to scan terrain for excavation planning, and I think I could use a similar approach for mapping out the local light pollution. My objective is to make a fairly detailed local map that will clearly show sources of skyglow in a fairly defensible and comparable fashion. And also not to spend any money, of course 🙂

My first thought was to take a survey-grade GPS receiver I've got lying about and assemble that alongside a cheap machine vision camera with a narrow field of view lens of some form pointing straight up, with some shielding to prevent stray light from headlights creeping in. Potentially also an infrared temperature sensor to let me measure cloud cover in some form, since that'd have a direct impact. The MV camera I could lock off in terms of exposure time, gain, etc. I can assemble this onto a magnetic roof mount on my car and drive around, logging data on a laptop in the car. I don't have many streetlights around but I figure I can probably exclude those in post if they're sufficiently bright compared to the rest.

However, thought I'd ask if anyone's done anything similar and if there's any more sensible approaches to consider - should I just use a SQM instead of the camera? Is the approach of measuring the sky directly above a sensible one? Should I consider angular measurements? Any other suggestions?

[vlaiv]

I think that you have all the gear that you need to do this - it just takes a bit of fiddling with the data that you capture in order to turn it into something that is useful.

You have ASI120MC, and I presume you have small lens that comes with it - all sky lens? If not - it is really not that expensive to get one. With it you can create images like this:

That gives you coverage of whole sky from certain vantage point. People sometimes use such images to create LP maps for their location - like this:

You could mount such system on your car and then gather similar images from different locations, and then it is down to interpreting that data - you could do some sort of 3D visualization of that data as for each location you have total LP coming from a certain direction - multiple such points would help build a model of LP in certain volume of sky - and then you could try to simulate ground lighting that produces such sky glow.

I mean this is advanced stuff as you would need to model scattering in atmosphere and types of illumination from the ground, but just a set of images like above one with map and direction of main sources of LP - and coordinates where those directions intersect could point out to particular LP source (a bit like triangulation of radio sources).

For example, in above image it is evident that strongest LP comes from about 350° (which is not surprising as it is direction of my home town for location above image was taken and it glows bright ) - but in your images - that would be one line for intersection on the map.

 

[PeterW]

Triangulation of all sky images would be a good start. SQM only give you zenith data and that can vary by transparency and the like. There is mention that LED are not well measured with SQM, thiugh my garden sky feels darker since local full cutoff  LED have been fitted.

Good luck

Peter