NOAA-21 VIIRS: Global Near Real-Time Ocean Remote Sensing Reflectance

Near real-time (NRT) remote sensing reflectance (RRS) data from the NOAA-21 satellite's VIIRS instrument provides a snapshot of ocean optical properties within a single orbit. The Ocean Biology DAAC produces this foundational observable, which is used to derive products like chlorophyll-a concentration and water clarity. Users must apply quality flags for land, cloud, and sun glint, especially in complex coastal waters.

Use Cases

• Retrieving chlorophyll-a concentration (chlor_a) based on the foundational Rrs_λ variable.
• Estimating water clarity (Kd_490) based on remote sensing reflectance at multiple wavelengths.
• Developing and validating ocean color algorithms based on the Rrs suite of geophysical variables.
• Monitoring water quality for ecosystem applications based on reflectance data flagged for atmospheric conditions.

Strengths

• Provides near real-time (NRT) data, offering a snapshot from a short time period within a single orbit.
• Includes per-file quality flags for factors like land, cloud, sun glint, and high aerosol, as mentioned in the description.
• Serves as the foundational observable (Rrs) for retrieving multiple derived oceanographic products.

Limitations

• Description metadata is limited; actual data quality requires manual inspection after download.
• The NRT processing uses less-than-optimal ancillary data and calibration, as stated in the description.
• Column-level documentation is absent; field semantics must be inferred after download.

Provenance

Source

Ocean Biology DAAC (OB_CLOUD) via NASA Earthdata.

Collection Method

Satellite remote sensing from the NOAA-21 VIIRS instrument.

Freshness

Near real-time (NRT); specific update frequency is unknown.

Geography

Global