6 CSIEM : satellite
6.1 Overview
Satellite remote sensing provides a critical independent data source for the CSIEM platform, offering spatially continuous observations of water quality, sea surface temperature, and ocean colour across the Cockburn Sound region and broader Perth coastal waters. Unlike in-situ monitoring, which is limited to fixed stations and discrete sampling events, satellite products deliver synoptic coverage at regular intervals, enabling the detection of spatial patterns and transient events — such as algal blooms, turbidity plumes, and marine heatwaves — that may be missed by point-based measurements.
Within the CSIEM framework, satellite data serve three primary roles:
Model validation: Satellite-derived fields (e.g., chlorophyll-a, SST, turbidity) provide independent benchmarks against which model predictions can be assessed over the full spatial domain, complementing comparisons at individual monitoring stations.
Near-real-time monitoring: Automated data pipelines harvest and process the latest satellite imagery, supporting operational awareness of environmental conditions in Cockburn Sound and surrounds.
Long-term trend analysis: Multi-decadal SST records and growing archives of ocean colour data enable assessment of climate-driven changes such as marine heatwave frequency and intensity.
The key satellite products integrated into CSIEM are: Sentinel-2 multispectral imagery for high-resolution water quality retrieval, GHRSST sea surface temperature products, and Sentinel-3 ocean colour data. The processing workflows, derived products, and associated dashboards are described in the following sections.
6.2 Sentinel-2 water quality processing
The European Space Agency’s Sentinel-2 mission provides multispectral imagery at 10 m spatial resolution with a revisit time of approximately 5 days, making it well suited for monitoring optically complex coastal waters such as those in Cockburn Sound.
6.2.1 Processing workflow
Raw Sentinel-2 Level-1C (top-of-atmosphere) imagery is processed using the Case-2 Regional Coast Colour (C2RCC) algorithm, which is specifically designed for optically complex (Case-2) waters where standard open-ocean atmospheric correction algorithms perform poorly. The C2RCC processor derives water-leaving reflectance from which several biogeochemical products are estimated:
- Chlorophyll-a (chl-a): An indicator of phytoplankton biomass in the surface layer.
- Total suspended matter (TSM): A measure of particulate loading, relevant to turbidity and light attenuation.
- Coloured dissolved organic matter (CDOM): Indicative of dissolved organic inputs, including from terrestrial sources and riverine plumes.
- True colour composites: RGB imagery for visual identification of bloom events, sediment plumes, and vessel movements.
6.2.2 Bottom reflectance masking
In shallow coastal waters, benthic substrates (e.g., sand, seagrass) can contribute significantly to the water-leaving signal, leading to erroneous retrievals of water column properties. To address this, a bottom reflectance masking layer has been developed that, when enabled, automatically excludes shallow-water pixels influenced by benthic optical signals. This is essential for accurate retrieval of chl-a and TSM in the optically shallow areas of Cockburn Sound and Owen Anchorage.
6.2.3 Automation and reproducibility
The entire data pipeline — from automatic downloading of Sentinel-2 imagery to processing and display — has been fully automated and documented. Users can reproduce the workflow independently by following the tutorials and accessing the source code provided via:
- Documentation: sentinel2-water-quality.readthedocs.io
- Source code: Available on the SEAF-CS GitHub organisation
6.3 Sea surface temperature
Two satellite-derived SST products are integrated into the CSIEM platform, providing complementary temporal and spatial coverage:
- GHRSST (Group for High Resolution Sea Surface Temperature): A high-resolution product (~1.1 km) available from 2002 onwards, suitable for resolving fine-scale SST gradients in the coastal zone.
- CMEMS (Copernicus Marine Environment Monitoring Service): A long-term product (~5 km resolution) available from 1982 onwards, providing the extended baseline required for climatological analyses.
6.3.1 Marine heatwave detection
The SST data are used within a Marine Heatwave (MHW) analysis framework, adapted from the heatwaveR R package and based on the methodology of Hobday et al. (2016). The analysis app provides customisable statistical parameters, including temperature thresholds and minimum duration criteria, for identifying and categorising MHW events. Key outputs include event detection, exceedance statistics, and cumulative intensity metrics. SST data for this analysis are retrieved in near-real-time from the WAMSI Pawsey S3 data store.
6.4 Satellite dashboards
Several web-based dashboards have been developed to visualise satellite-derived products and facilitate integration with model outputs.
6.4.1 Leaflet satellite dashboard
A leaflet-based mapping dashboard integrates Sentinel-2 water quality products at 10 m resolution, GHRSST SST at 1 km resolution, and CSIEM modelled currents as velocity vectors. Together, these layers provide a multi-source view of marine ecosystem dynamics in the region. The dashboard is available at: csiemdash-leaflet.seaf.org.au.
The dashboard is designed for monitoring biogeochemical variables (chl-a, TSM, CDOM), SST, and true colour imagery. These products are particularly effective for identifying bloom dynamics, current-driven transport patterns, and river plume dispersal.
6.4.2 Regional satellite data harvesting
A broader regional dashboard harvests and displays satellite data across the Perth coastal zone, supporting both research and operational monitoring needs. This is accessible at: csiemdash-sat.seaf.org.au.
6.4.2.1 Available satellite data sources and products
The regional data harvesting system integrates satellite observations and model outputs from multiple international providers, organized by sensor type and offering comprehensive spatial and temporal coverage of marine biogeochemical and physical parameters:
Ocean Colour Sensors
Globcolor (merged multi-sensor product, 4 km resolution, daily frequency): A composite product combining data from multiple ocean colour satellites. Multi-sensor products (SeaWiFS, MODIS, MERIS, VIIRS-SNPP & JPSS1, OLCI-S3A & S3B) and OLCI-only products (S3A & S3B) provide comprehensive biogeochemical parameters including: Chlorophyll-a (CHL), Chlorophyll-a gradient (CHL_gradient), Phytoplankton Functional Types and sizes (PFT), Suspended Matter (SPM), Secchi Transparency Depth (ZSD), Diffuse Attenuation coefficient (KD490), Particulate Backscattering (BBP), Absorption coefficient (CDM), and Remote Sensing Reflectance (RRS). Distributed by the European Space Agency (ESA).
Sentinel-3 OLCI (Ocean and Land Colour Instrument, 300 m resolution, daily frequency): High-resolution ocean colour imagery from the ESA providing chlorophyll-a retrievals suited for coastal waters with enhanced spatial detail for monitoring nearshore dynamics.
MODIS (Moderate Resolution Imaging Spectroradiometer, 4 km resolution, monthly frequency): NASA satellite providing particulate organic carbon (POC), particulate inorganic carbon (PIC), and photosynthetically active radiation (PAR), supporting primary productivity and carbon cycle assessments.
Sea Surface Temperature Sensors
OSTIA (Operational Sea Surface Temperature and Sea Ice Analysis, ~5 km resolution, daily frequency): Blended product from the UK Met Office derived from multiple satellite and in-situ sources, providing continuous thermal data across regional waters.
GHRSST/MUR (Group for High Resolution Sea Surface Temperature, ~1 km resolution, daily frequency): The Version 4 Multiscale Ultrahigh Resolution (MUR) L4 analysis is based on nighttime GHRSST L2P skin and subskin SST observations from multiple instruments, including NASA AMSR-E, JAXA AMSR2 on GCOM-W1, MODIS Aqua and Terra, the US Navy WindSat radiometer, AVHRR sensors on several NOAA satellites, and in situ SST observations from the NOAA iQuam project. Ice concentration data are sourced from the EUMETSAT OSI SAF High Latitude Processing Center archives and are used to improve SST parameterization at high latitudes.
Biogeochemical and Physical Model Outputs
PISCES (biogeochemical model, Mercator Ocean International, ~25 km resolution, daily frequency): Simulated fields including net primary production (NPPV), oxygen (O₂), iron (Fe), nitrate (NO₃), phosphate (PO₄), silicate (Si), light attenuation (KD), dissolved inorganic carbon (DIC), pH, total alkalinity (TALK), partial pressure of CO₂ (pCO₂), and phytoplankton types with chlorophyll.
SEAPODYM (ecosystem model, ~9 km resolution, daily frequency): Provides simulated primary productivity and zooplankton biomass supporting ecosystem monitoring and fisheries-relevant assessments.
NEMO (hydrodynamic model, ~9 km resolution, 6-hourly frequency): Delivers physical oceanographic fields including salinity and currents underlying biogeochemical model runs.
This multi-sensor and multi-source integration enables synergistic use of complementary satellite observations and model estimates, enhancing the temporal frequency, spatial resolution, and parameter diversity available for monitoring and validating coastal marine processes.
6.4.2.2 Detailed product-variable inventory
For transparency and reproducibility, the regional data harvesting configuration can also be described using a provider-product-variable hierarchy with units:
European Space Agency (ESA)
|-- Globcolor (4 km, daily)
| |-- Reflectance
| | |-- RRS412 (Remote Sensing Reflectance at 412 nm) [sr^-1]
| | |-- RRS443 (Remote Sensing Reflectance at 443 nm) [sr^-1]
| | |-- RRS490 (Remote Sensing Reflectance at 490 nm) [sr^-1]
| | |-- RRS555 (Remote Sensing Reflectance at 555 nm) [sr^-1]
| | `-- RRS670 (Remote Sensing Reflectance at 670 nm) [sr^-1]
| |-- PP [mg C m^-2 d^-1]
| |-- Optics
| | |-- BBP (Backscattering coefficient) [m^-1]
| | `-- CDM (Colored Dissolved Organic Matter) [m^-1]
| |-- Transparency
| | |-- KD490 (Diffuse attenuation coefficient at 490 nm) [m^-1]
| | |-- ZSD (Secchi disk depth) [m]
| | `-- SPM (Suspended Particulate Matter) [g m^-3]
| `-- Plankton
| |-- CHL (Chlorophyll concentration) [mg m^-3]
| |-- DIATO (Diatoms) [mg m^-3]
| |-- DINO (Dinoflagellates) [mg m^-3]
| |-- GREEN (Green algae) [mg m^-3]
| |-- HAPTO (Haptophytes) [mg m^-3]
| |-- MICRO (Microplankton) [mg m^-3]
| |-- NANO (Nanoplankton) [mg m^-3]
| |-- PICO (Picoplankton) [mg m^-3]
| |-- PROCHLO (Prochlorococcus) [mg m^-3]
| `-- PROKAR (Prokaryotes) [mg m^-3]
`-- Sentinel-3 OLCI (300 m, daily)
`-- CHL [mg m^-3]
UK Met Office (UKMO)
`-- OSTIA (~5 km, daily)
`-- Temperature [K]
NASA
|-- GHRSST MUR (~1 km, daily)
| `-- SST [deg C]
`-- MODIS (monthly)
|-- POC (Particulate Organic Carbon) [mg m^-3]
|-- PIC (Particulate Inorganic Carbon) [mg m^-3]
`-- PAR (Photosynthetically Active Radiation) [Einstein m^-2 d^-1]
Mercator Ocean International (MOI)
`-- Model products
|-- PISCES (~25 km, daily)
| |-- Bio
| | |-- Net Primary Production (NPPV) [mg C m^-3 d^-1]
| | `-- Oxygen (O2) [mmol O2 m^-3]
| |-- Nutrients
| | |-- Iron (Fe) [mmol Fe m^-3]
| | |-- Nitrate (NO3) [mmol N m^-3]
| | |-- Phosphate (PO4) [mmol P m^-3]
| | `-- Silicate (Si) [mmol Si m^-3]
| |-- Optics
| | `-- Light Attenuation Coefficient (KD) [m^-1]
| |-- Carbonate system
| | |-- Dissolved Inorganic Carbon (DIC) [mmol C m^-3]
| | |-- pH [-]
| | `-- Total Alkalinity (TALK) [mmol eq m^-3]
| |-- CO2
| | `-- Partial Pressure of CO2 (pCO2) [Pa]
| `-- PFTs
| |-- Chlorophyll (Chl) [mg m^-3]
| `-- Phytoplankton (Phyc) [mmol m^-3]
|-- SEAPODYM (~9 km, daily)
| `-- Biomass
| |-- PP (Primary productivity) [mg C m^-2 d^-1]
| `-- ZOO (Zooplankton) [mg C m^-2]
`-- NEMO (~9 km, 6-hourly)
`-- Salinity [10^-3]6.4.3 Marine Heatwave Analysis
Output from the satellite data series is used to inform the Marine Heatwave analysis for Cockburn Sound. See Chapter 18 for MHW-specific outputs such as exceedance plots and cumulative intensity metrics. Events are categorised from moderate to extreme following the Hobday et al. (2016) classification.
6.5 Summary
Satellite remote sensing is an integral component of the CSIEM platform, providing spatially continuous, independent observations that complement in-situ measurements and model predictions. The automated Sentinel-2 processing pipeline delivers high-resolution water quality products with bottom reflectance masking suited to the shallow waters of Cockburn Sound. Long-term SST records support marine heatwave detection and climate trend analysis. Together with the interactive dashboards, these capabilities support both model validation and operational environmental monitoring for the region.