Satellite–in-situ matchups

Satellite–in-situ matchups#

Besides pairing two satellites (see Finding matchups), eomatch can match satellite products against a fixed in-situ (ground-based) site, such as a RadCalNet or HYPERNETS station. The result is the same MatchupEvent / Matchup objects, so cataloguing, enrichment and dataset building work unchanged.

How it differs from satellite–satellite matching#

  • There is no orbit propagation. The site’s fixed location, not a crossover, defines where to search.

  • Sat2InSituMUFinder queries the satellite collection over the site’s registered region of interest for the whole configured time window, then groups the returned products into events: passes closer together than time_diff_threshold form one event.

  • For each event, every satellite product is paired with the in-situ products that are within time_diff_threshold of it and overlap its footprint. Products are compared as time intervals, so a satellite pass anywhere inside an in-situ product’s multi-hour recording window counts as a zero gap. A satellite product with no in-situ product close enough in time gets no matchup.

Configuration#

platforms and collections are paired by position, and must contain exactly one satellite and one in-situ collection. The platform paired with the in-situ collection is the site name:

platforms: S2A, GONA
collections: S2_MSI_L1C, RCN_BOA
start_time: "2024-05-21 00:00:00"
end_time:   "2024-05-24 00:00:00"
time_diff_threshold: 1800          # seconds

provider_by_collection (see Pinning a provider per collection) applies to the satellite query as it does for satellite–satellite matching.

Running the finder#

from eomatch import EOMatchContext
from eomatch.find_and_catalogue import find_and_catalogue_insitu

In [1]: In [1]: ctx = EOMatchContext("insitu_config.yaml")

In [2]: In [2]: catalogue = find_and_catalogue_insitu(context=ctx, path="/data/insitu_catalogue")

In [3]: In [3]: event = catalogue.get_events()[0]

In [4]: In [4]: [p.collection for p in event.matchup_set[0].products]

In [5]: Out[4]: ['S2_MSI_L1C', 'RCN_BOA']

find_and_catalogue_insitu() is the in-situ counterpart of find_and_catalogue(): it runs the finder and saves the events and matchups to a STAC catalogue. To work with the events without cataloguing, use the finder directly:

from eomatch.finder.sat2insitu import Sat2InSituMUFinder

events = Sat2InSituMUFinder(context=ctx).finder()

Filtering on in-situ data quality#

A matchup passing the time and footprint checks can still have no valid in-situ sample near the crossover. Add the insitu_time_diff enricher (see Enriching matchup metadata) to record the gap to the nearest valid sample, then filter on it:

from eomatch.enrich import enrich
from eomatch.enrich.insitu_time_diff import insitu_time_diff

In [6]: In [1]: enrich(catalogue, enrichers=[insitu_time_diff])

In [7]: Out[1]: 12

In [8]: In [2]: nearby = {"insitu_time_diff_nearest_s": {"lt": 1800}}

In [9]: In [3]: events = catalogue.get_events(properties=nearby)