Shade Path

Description

Calculates and plots the path used to create targeted shade, or formed by a fixed sunshade, for 24 hours on given date(s). Also records insolation for the same time periods.

It is used to calculate and visualise either:

• The path an airborne craft would need to follow to shade a specific point on the Earth's surface
• The path followed by shade cast from a fixed point in the air

It needs be supplied with an altitude in km, the location of a point on the Earth's surface, one-or-more dates, and a time-interval.

Usage

Initiate the ShadePath object

myPath = ShadePath(latitude, longitude,target_altitude,mode)

Where:

• target_altitude is an alitude in kilometeres, e.g. 12
• mode is 'mobile' or 'static'
• latitude and longitude in degrees specify a location on the Earth's surface
  • In 'static' mode, this where a shade would be positioned
  • In 'mobile' mode, this is the target point on the ground

Traverse a Path (runCircuits)

myPath.runCircuits(dates,timezone_offset_string,interval)

Where:

• timezone_offset_string specifies the offset from UST at the target location, e.g. "-08:00"
• dates is a list of dates to include on the same plot, in standard form, e.g. "['2023-06-01','2023-06-20']"
• interval is the time interval used between plotting points on the path, in minutes
  • 10 minutes makes a reasonably smooth plot

Results

runCircuits populates a 'results' data frame on the ShadePath object (e.g. myPath.results), storing the calculated attributes at each time interval for each date, which contains the following key columns:

column label	data type	description
datetime	datetime	UTC datetime
local-time	datetime	local datetime
aboveHorizon	boolean	1 if the sun is above the horizon, 0 if it's below
solarAltitude	float	solar altitude angle in degrees
azimuth	float	solar azimuth angle in degrees
insolation	float	Insolation in W/m2
chord	float	distance from the target to the point where the line reaches the given altitude
distance	float	chord distance adjusted to account for the curvature of the earth
shading-longitude	float	longitude in degrees, meaning dependent on mode
shading-latitude	float	latitude in degrees, meaning dependent on mode

Create a Map of the Path (staticMap)

myMap = myPath.staticMap(line_colours,dot_colour)

Where:

• line_colours is a list of colours to be used for the paths for each date in the list of dates
  • i.e. there should be the same number of colours as dates
• dot_colour is the colour to be used for
  • the position of the shade in 'static' mode
  • the position of the shading target in 'mobile' mode

Fixed attributes that could/should be parameters:

• Projection: Uses an azimuthal equidistant projection.
• Area around the target location: Uses 0.5 degrees range in latitude and longitude

Returns a Basemap object, although this is only needed if further map manipulation is required.

Examples of Use

run-shade-path.py

run-shade-path.py is an example script used to run Shade Path

It creates two plots for the same two dates, at the same fixed location on the Earth's surface:

1. Path followed by a autonomous airborne sunshade targeting this location
2. Shade cast by an airborne sunshade tethered at this location

insolation_plots.ipynb

Jupiter notebook demonstrating how to create a plot of insolation

Dependencies

Uses the following Python modules:

• Basemap
  • see the page installing-basemap.md
• Great Circle Calculator (gcc)
• Pandas
• Plotly
• Pysolar