mursst.md

GHRSST COGs (MURSST)

https://source.coop/repositories/ausantarctic/ghrsst-mur-v2/description

library(terra)

files <- arrow::read_parquet("https://data.source.coop/ausantarctic/ghrsst-mur-v2/ghrsst-mur-v2.parquet")

## it's a STAC catalogue
f <- sprintf("/vsicurl/%s", tail(files$assets$analysed_sst$href, 1))
r <- r <- rast(f)

## need fairly recent terra for this else `project(r, rast(), by_util = TRUE)`
plot(r)
title(substr(basename(f), 1, 8))

## not fast here, could be improved for sure
str(extract(r, vect(cbind(147, c(-45, -55)), type = "l")))
#'data.frame':   1001 obs. of  2 variables:
# $ ID                                                                    : num  1 1 1 1 1 1 1 1 1 1 ...
# $ 20250315090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1_analysed_sst: num  16.7 16.7 16.7 16.7 16.7 ...
 

The 'analysed_sst' files are templated by

template <- "https://data.source.coop/ausantarctic/ghrsst-mur-v2/{format(date, '%Y/%m/%d')}/{format(date, '%Y%m%d')}090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1_analysed_sst.tif"

## so for a specific date
date <- as.Date("2025-02-14")
(url <- glue::glue(template))

Strictly we should check the catalogue

catalog <- arrow::read_parquet("https://data.source.coop/ausantarctic/ghrsst-mur-v2/ghrsst-mur-v2.parquet")
if (! url %in% catalog$assets$analysed_sst$href) {
  message("file does not exist, check available dates")
} else {
 dsn <- glue::glue("/vsicurl/{url}")
}

library(terra)
(sst <- rast(dsn))

## or
library(gdalraster)
(ds <- new(GDALRaster, dsn))

## or
library(stars)
(sstars <- read_stars(dsn, proxy = TRUE))

To crop with the terra package use crop

crop(sst, ext(130, 150, -55, -42))

or more generally, project (by util is very important for COG)

project(sst, rast(ext(130, 150, -55, -42), res = res(sst)), by_util = TRUE)

We can change crs and resolution as desired

target <- rast(ext(c(-1, 1, -1, 1) * 6e5), res = 1000, crs = "+proj=laea +lon_0=147 +lat_0=-45")
project(sst, target, by_util = TRUE)

with rstac on a json item

rstac::read_stac("https://data.source.coop/ausantarctic/ghrsst-mur-v2/2025/02/09/20250209090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.stac-item.json")


###Item
- id: 20250209090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.stac-item
- collection: ghrsst-mur-v2
- bbox: xmin: -179.99500, ymin: -89.99500, xmax: 180.00500, ymax: 89.99500
- datetime: 2025-02-09T00:00:00Z
- assets: analysed_sst, analysis_error, mask, sea_ice_fraction, sst_anomaly
- item's fields: assets, bbox, collection, geometry, id, links, properties, stac_extensions, stac_version, type