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Extracts Land Surface Temperature (LST) from MODIS MOD11A1

Source: R/l4h_surface_temp.R
l4h_surface_temp.Rd

Extracts daytime or nighttime Land Surface Temperature (LST) for a user-defined region and time range using the MODIS MOD11A1.061 product. The function supports summarizing the temperature data over each date (or each month) using a selected statistic (e.g., mean or median).

Usage

l4h_surface_temp(
  from,
  to,
  region,
  band = "day",
  level = "strict",
  by = "day",
  scale = 1000,
  stat = "mean",
  sf = TRUE,
  quiet = FALSE,
  force = FALSE,
  ...
)

Arguments

from

Character or Date. Start date of the analysis (e.g., "2020-01-01").

to

Character or Date. End date of the analysis (e.g., "2020-12-31").

region

A spatial object defining the region of interest. Accepts an sf, sfc, or SpatVector object.

band

Character. LST type to extract: "day" (LST_Day_1km) or "night" (LST_Night_1km). Default is "day".

level

Character. Quality filter level to apply to MODIS LST pixels. Use "strict" to retain only high-quality observations (QA bits 0-1 equal to 00), or "moderate" to allow both high and acceptable quality (QA bits 0-1 equal to 00 or 01). Default is "moderate".

by

Character. Temporal resolution of the output. One of "day" (default, one value per available daily image) or "month". When "month", cloud-masked daily images within each calendar month are combined server-side with the reducer selected in stat (mean, median, min or max) before the spatial extraction, so masked (cloudy) pixels do not count as zeros or missing days — they are simply excluded from that month's reducer.

scale

Numeric. Spatial resolution in meters. Default is 1000 (native resolution).

stat

Character. Summary statistic to apply. One of "mean", "median", "min", "max". Used as the spatial reducer passed to ee_extract() for every by value, and additionally as the temporal reducer across days within a month when by = "month".

sf

Logical. If TRUE, returns an sf object; if FALSE, returns a tibble. Default is TRUE.

quiet

Logical. If TRUE, suppresses progress bars and messages. Default is FALSE.

force

Logical. If TRUE, skips the representativity check (polygons smaller than 1 pixel are still extracted, only a warning is issued). Default is FALSE.

...

Additional arguments passed to rgee::ee_extract().

Value

A sf or tibble object with LST values (in degrees Celsius) extracted from MODIS MOD11A1, at daily or monthly resolution depending on by.

Details

The MODIS MOD11A1.061 product provides daily Land Surface Temperature and quality information. This function filters out low-quality or cloud-contaminated pixels based on the QC_Day or QC_Night band.

When by = "month", for each calendar month in [from, to] the function:

  1. Filters the daily collection to that month.

  2. Applies the same quality mask used for daily extraction to every image.

  3. Reduces the masked images to a single monthly image using the reducer implied by stat.

Because masking happens before reducing, a cloudy day never drags the monthly value down or up — it simply does not contribute a pixel to that month's calculation.

LST values are originally stored as Kelvin multiplied by 0.02. This function automatically converts them to degrees Celsius using the formula: LST = (value x 0.02) - 273.15.

Credits

Pioneering geospatial health analytics and open-science tools. Developed by the Innovalab Team. For more information, send an email to imt.innovlab@oficinas-upch.pe.

References

Wan, Z., Hook, S., & Hulley, G. (2015). MOD11A1 MODIS/Terra Land Surface Temperature and Emissivity Daily L3 Global 1km SIN Grid V006 (Version 6.1). NASA EOSDIS Land Processes DAAC. doi:10.5067/MODIS/MOD11A1.061

MODIS MOD11A1.061 - Google Earth Engine Dataset Catalog. https://developers.google.com/earth-engine/datasets/catalog/MODIS_061_MOD11A1

Examples

# \donttest{
if (interactive()) {
library(land4health)
ee_Initialize()

region <- st_as_sf(st_sfc(
  st_polygon(list(matrix(c(
    -74.1, -4.4,
    -74.1, -3.7,
    -73.2, -3.7,
    -73.2, -4.4,
    -74.1, -4.4
  ), ncol = 2, byrow = TRUE))),
  crs = 4326
))

# Daily (unchanged default behaviour)
lst_day <- l4h_surface_temp(
  from = "2020-01-01", to = "2020-12-31",
  region = region, band = "day", stat = "mean")

# Monthly
lst_month <- l4h_surface_temp(
  from = "2020-01-01", to = "2020-12-31",
  region = region, band = "day", stat = "mean", by = "month")

head(lst_month)
}
# }