NOAA MSL12 Ocean Color

2023-03-12 22:36| 来源: 网络整理| 查看: 265

The current VIIRS SNPP science quality collection, released in CoastWatch as of 07 August 2017, is produced from MSL12 v1.2* using OC-SDR v04. VIIRS NOAA-20 Science Quality is currently in development. NOAA-20 Near real-time is already available.

Ocean Color satellite sensors measure visible light at specific wavelengths which leaves the surface of the ocean and arrives at the top of the atmosphere where the sensor is located. nLw, can be calculated. nLws are used to derive other ocean properties such as the concentration of chlorophyll-a (chlor-a, chlora, or sometimes chl , which is the green pigment responsible for photosynthesis and therefore and indicator of the amount of phytoplankton biomass in the ocean water) and the coefficients for attenuation of downwelling irradiance (Kd(PAR) and Kd(490) which are related to water clarity).

The ocean color datasets described here are from the Visible Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the Suomi-NPP satellite (SNPP) which was launched in November 2011 and aboard the NOAA-20 which was launched in November 2017. The ocean color science quality collection differ in several ways from the near real-time products (Table 1).

*Note that the metadata in the NetCDF files show v1.20 from the beginning of the collection (2 Jan. 2012) up tthrough 24 April 2017 and v1.21 from 25 April 2017 forward. This version change did not affect retrieval values for the standard products served by CoastWatch.

Table 1. Comparison of primary processing differences for VIIRS SNPP near real time versus science quality ocean color data.

Parameter Near real-time Science Quality Latency ~12 hours (best effort) Delayed 15 days Sensor Data Record (SDR) IDPS Operational SDR SDR produced by the NOAA/STAR ocean color team Ancillary Data Predicted Assimilated Spatial Coverage May have gaps As complete as possible

Standard VIIRS SNPP ocean color data Level 2 products from MSL12 v1.2(both near real-time and science quality) include:

Normalized water-leaving (nLw) radiance at 6 visible bands (nominal center wavelengths) M1 (410nm) M2 (443nm) M3 (486nm) M4 (551nm) M5 (671nm) I1 (638 nm) Chlorophyll-a concentration Diffuse attenuation coefficient at 490 nm (Kd(490)), and Diffuse attenuation coefficient of photosynthetically active radiation (Kd(PAR)) QA Score (a quantitative assessment of VIIRS ocean color performance with respect to an empirical catalog of in situ spectra, Wei et al., 2016; see reference tab)

See Table 2 for quick reference matrix of additional science quality VIIRS ocean color products. The Ocean Color Granule Selector is a tool to interactively preview, choose and download L2 granule files. Data files are in NetCDF4/CF but differ from past NOAA CoastWatch products in their use of hierarchical groups to store attributes, variables, and dimensions. CoastWatch Utilities Software has been updated to work with these files. Additional metadata can be obtained using THREDDS services such as ISO or OPeNDAP.

Table 2. Quick reference matrix of science quality VIIRS ocean color products available from CoastWatch.

Product Description Processing Level Nominal Spatial Resolution Chl-a nLws Kd(PAR) Kd(490) QA Score Daily granule global swath @750 m L2 750 m X X X X X Daily merged global sectorized * L3 750 m in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch not currently available 7-day merged global sectorized * L3 750 m in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch not currently available True monthly merged global sectorized * L3 750 m in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch in progress at CoastWatch not currently available Daily merged global single file L3 4 km X X X X X 7-day merged global single file L3 4 km X X X X X Monthly merged global single file L3 4 km X X X X X

*See Figure 1 for description and identification of sectors.

Level-2 science quality ocean color products are organized by Year and Day-of-the-Year. Filenames will appear as follows: V2017187003435_NPP_SCINIR_L2.nc where: V: Sensor VIIRS 2017: Year of observation (YYYY) 187: Day of year for the observation (DDD) 003435: Hour, minutes, and seconds of the start of observation (hhmmss) in UTC NPP: Spacecraft S-NPP SCINIR: Sensor data record source and environmental data record algorithm. Indicates the standard Science Quality output for distribution L2: Processing level. L2 includes calibrated and geolocated geophysical products

Figure 1. Twenty-four sectors identified for file naming convention. Sectors enable downloads of select subset regions from global high resolution VIIRS ocean color science quality data.

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