Magnitude Distribution

Mix.install([{:tucan, "~> 0.4.1"}, {:kino_vega_lite, "~> 0.1.8"}])

Extracting EO Observations From MMT9 Data

MMT9 Data

MMT9 is a Russian optical network that collects high-rate photometry on LEO satellites. Data can be found at http://mmt.favor2.info/satellites

defmodule MMT9Parser do
  def parse_line(line) do
    # data format | Date Time StdMag Mag Filter Penumbra Distance Phase Channel Track
    fields = String.split(line)
    try do
      {:ok, datetime, 0} = DateTime.from_iso8601(Enum.at(fields, 0) <> "T" <> Enum.at(fields, 1) <> "Z")
      %{
        epoch: datetime,
        std_mag: String.to_float(Enum.at(fields, 2)),
        raw_mag: String.to_float(Enum.at(fields, 3)),
        phase: String.to_float(Enum.at(fields, 7))
      }
    rescue
      ArgumentError -> nil
      MatchError -> nil
    end
  end

  def group_obs_by_month_and_phase(obs, month, phase_min, phase_max) do
    mags = obs
      |> Enum.filter(fn o -> o.epoch.month == month &amp;&amp; o.phase < phase_max &amp;&amp; o.phase> phase_min end)
      |> Enum.map(fn k -> k.raw_mag end)
      |> Enum.reject(&amp;is_nil(&amp;1))
    if length(mags) == 0 do
      nil
    else
      %{
        month: month,
        phase: phase_min,
        avg_mag: Enum.sum(mags) / length(mags)
      }
    end
  end

  def group_obs_by_phase(obs, phase_min, phase_max) do
    center_phase = (phase_min + phase_max) / 2
    obs
      |> Enum.filter(fn o -> o.phase < phase_max &amp;&amp; o.phase > phase_min end)
      |> Enum.map(fn k -> %{std_mag: k.std_mag, phase: center_phase} end)
      |> Enum.reject(&amp;is_nil(&amp;1.std_mag))
  end
end


file_path = ""

{:ok, text} = File.read(file_path)

# split by line- each data point is on its own line
lines = text |> String.split("\n") |> Enum.drop(7) # first 7 lines are header data

eo_obs = Enum.map(lines, fn line -> Task.async(MMT9Parser, :parse_line, [line]) end)
  |> Enum.map(&amp;Task.await(&amp;1))
  |> Enum.reject(&amp;is_nil(&amp;1))

IO.puts("Parsed data file of #{length(eo_obs)} lines")

# now group data by month & phase (1deg bins)
grouped_eo_obs = Enum.flat_map(1..12, fn mo ->
  for p <- 0..35 do
    Task.async(MMT9Parser, :group_obs_by_month_and_phase, [eo_obs, mo, p * 5, p * 5 + 5])
  end
  |> Enum.map(&amp;Task.await(&amp;1, :infinity))
  |> Enum.reject(&amp;is_nil(&amp;1))
end
)

obs_by_phase = Enum.map(0..179, fn p ->
  Task.async(MMT9Parser, :group_obs_by_phase, [eo_obs, p, p + 1])
end)
|> Enum.flat_map(&amp;Task.await(&amp;1, :infinity))
|> Enum.reject(&amp;is_nil(&amp;1))

# full raw distribution
multivariate = Tucan.heatmap(grouped_eo_obs, "month", "phase", "avg_mag")
  |> Tucan.set_title("Std. Magnitude by Time of Year & Phase Angle")
  |> Tucan.set_height(600)
  |> Tucan.set_width(400)

# "photometric signature"
univariate = Tucan.density(eo_obs, "std_mag")
  |> Tucan.set_title("Normalized Magnitude Distribution")
  |> Tucan.set_height(600)
  |> Tucan.set_width(600)

# std. mag over phase- deviations from flat line indicate error from lambertian sphere normalization,
# error/stdev indicates variability (likely due to intrinsic rotation)
phaseplot = Tucan.errorband(obs_by_phase, "phase", "std_mag")
  |> Tucan.set_title("Std. Mag Over Solar Phase Angle")
  |> Tucan.set_height(400)
  |> Tucan.set_width(1000)

distributions = Tucan.hconcat([univariate, multivariate])
Tucan.vconcat([distributions, phaseplot])