ntl_index: Index nighttime-light values to a baseline period

In lightson: Download and Analyse Nighttime Lights Satellite Data

Index nighttime-light values to a baseline period

Description

Converts each group's values to an index where its baseline observation is 100. This is useful for comparing changes between sources with different units, but does not make their absolute levels comparable.

Usage

ntl_index(
  panel,
  baseline,
  group_cols = NULL,
  time_col = "year",
  value_col = "mean_radiance",
  index_col = "ntl_index"
)

Arguments

panel	Data frame containing nighttime-light observations.
baseline	Baseline value in time_col, such as 2020 or an ISO date.
group_cols	Grouping columns. If omitted, uses source when present plus region_id or state.
time_col	Time column name. Defaults to "year".
value_col	Value column name. Defaults to "mean_radiance".
index_col	Name for the new index column.

Value

panel with an additional numeric index column.

Examples

panel <- data.frame(
  region_id = rep(c("a", "b"), each = 3),
  year = rep(2020:2022, 2),
  mean_radiance = c(10, 12, 15, 4, 4, 5)
)
ntl_index(panel, baseline = 2020)

lightson documentation built on Nov. 3, 2026, 5:07 p.m.