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Description

The ILW suite provides inland-water extractions for lakes and reservoirs across the contiguous U.S. (CONUS) and Alaska. ILW delivers Rayleigh-corrected surface reflectance (ρs, unitless) and the Cyanobacteria Index (CI_cyano, unitless). The data target for MERIS and OLCI are 15,450 CONUS waterbodies (≥1 full-resolution 300 m OLCI pixel), >2,300 larger resolvable lakes (≥3 pixels), and 5,874 resolvable lakes in Alaska—created in collaboration with the CyAN program to reduce user processing and provide a standardized resource for inland-water algorithm development, validation, and trend analysis. PACE OCI ILW targets 117 CONUS lakes (≥3 pixels) and lakes across Alaska.

Geophysical variables in this suite include:
?~@? CI_cyano ?~@~S Cyanobacteria Index, cyanobacteria only (Wynne & Stumpf algorithm, 2013) (sr?~A?¹)
?~@? flags_habs ?~@~S Harmful Algal Bloom flags (unitless / bitmask)
?~@? rhos_λ ?~@~S Surface reflectance at wavelength λ (dimensionless)
• l2_flags – Level-2 Processing Flags (unitless / bitmask)

Product Summary

Platforms
ENVISAT
Instruments
MERIS
Spatial Extent

N: 90 S: -90 E: 180 W: -180

Location
UNITED STATES OF AMERICA
Coordinate System
CARTESIAN
Granule Spatial Representation
GEODETIC
Temporal Extent
2002-03-21 to 2012-05-09
Data Partner
Ocean Biology Processing Group (OBPG) ,
Ocean Biology Distributed Active Archive Center (OB.DAAC), Global Change Data Center, Earth Sciences Division, Science and Exploration Directorate, Goddard Space Flight Center, NASA (NASA/GSFC/SED/ESD/GCDC/OB.DAAC)
Concept ID
C3433948159-OB_CLOUD
Data State
COMPLETE
Number of Files/Granules
22316
Processing Level
2
Published
Updated
Science Keywords
CYANOBACTERIA (BLUE-GREEN ALGAE) ,
HARMFUL ALGAL BLOOM (HABs) ,
Water Color ,
Lakes/Reservoirs ,
Wetlands ,
Ground Water ,
Rivers/Streams

Citation

Citation is critically important for dataset documentation and discovery. This dataset is openly shared, without restriction, in accordance with the EOSDIS Data Use and Citation Guidance.

Copy Citation

NASA Ocean Biology Processing Group. (2025). ENVISAT MERIS Regional Inland Waters (ILW) Data, version 5.0 [Data set]. NASA Ocean Biology Distributed Active Archive Center. https://doi.org/10.5067/ENVISAT/MERIS/L2/ILW/5.0 Date Accessed: 2026-04-21

Variables

The table below lists the variables contained within a single granule for this dataset. Variables often contain observed or derived geophysical measurements collected from a variety of sources, including remote sensing instruments on satellite and airborne platforms, field campaigns, in situ measurements, and model outputs. The terms variable, parameter, scientific data set, layer, and band have been used across NASA’s Earth science disciplines; however, variable is the designated nomenclature in NASA’s Common Metadata Repository (CMR). Variable metadata attributes such as Name, Description, Units, Data Type, Fill Value, Valid Range, and Scale Factor allow users to efficiently process and analyze the data. The full range of attributes may not be applicable to all variables. Additional information on variable attributes is typically available in the data, user guide, and/or other product documentation.

For questions on a specific variable, please use the Earthdata Forum.

Name Description Units Data Type Fill Value Valid Range Scale Factor Offset
geophysical_data/CI_cyano Cyanobacteria Index - cyanobacteria only Wynne, Stumpf algorithm 2013 sr^-1 float32 -32767 4.9999998736894E-5 to 0.050000000745058 N/A N/A
geophysical_data/flags_habs Harmful Algal Blooms flags for clouds and non-water N/A uint8 128 0 to 255 N/A N/A
geophysical_data/l2_flags Level-2 Processing Flags N/A int32 N/A -2147483648 to 2147483647 N/A N/A
geophysical_data/rhos_413 Surface reflectance at 413 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_443 Surface reflectance at 443 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_490 Surface reflectance at 490 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_510 Surface reflectance at 510 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_560 Surface reflectance at 560 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_620 Surface reflectance at 620 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_665 Surface reflectance at 665 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_681 Surface reflectance at 681 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_709 Surface reflectance at 709 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_754 Surface reflectance at 754 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_762 Surface reflectance at 762 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_779 Surface reflectance at 779 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_865 Surface reflectance at 865 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_885 Surface reflectance at 885 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
geophysical_data/rhos_900 Surface reflectance at 900 nm N/A float32 -32767 -0.050000000745058 to 1 N/A N/A
navigation_data/latitude Latitude degrees_north float32 -999 -90 to 90 N/A N/A
navigation_data/longitude Longitude degrees_east float32 -999 -180 to 180 N/A N/A
navigation_data/tilt Sensor tilt angle degree float32 -32767 -25 to 25 N/A N/A
scan_line_attributes/clat Center Latitude degrees_north float32 -999 -90 to 90 N/A N/A
scan_line_attributes/clon Center Longitude degrees_east float32 -999 -180 to 180 N/A N/A
scan_line_attributes/csol_z Center Solar Zenith Angle degree float32 -999 -90 to 90 N/A N/A
scan_line_attributes/day Scan day of year days int32 -32767 0 to 366 N/A N/A
scan_line_attributes/detnum Detector Number (zero-based) N/A int8 -1 0 to 25 N/A N/A
scan_line_attributes/elat Ending Latitude degrees_north float32 -999 -90 to 90 N/A N/A
scan_line_attributes/elon Ending Longitude degrees_east float32 -999 -180 to 180 N/A N/A
scan_line_attributes/msec Scan time, milliseconds of day milliseconds int32 -32767 0 to 86400000 N/A N/A
scan_line_attributes/mside Mirror Side (zero-based) N/A int8 -1 0 to 1 N/A N/A
scan_line_attributes/slat Starting Latitude degrees_north float32 -999 -90 to 90 N/A N/A
scan_line_attributes/slon Starting Longitude degrees_east float32 -999 -180 to 180 N/A N/A
scan_line_attributes/time scan line time in seconds since 1970-1-1 seconds since 1970-1-1 float64 -32767 N/A N/A N/A
scan_line_attributes/year Scan year years int32 -32767 1900 to 2100 N/A N/A
sensor_band_parameters/aw Band-pass averaged absorption coefficient for seawater m^-1 float32 -32767 9.9999997473788E-5 to 5 N/A N/A
sensor_band_parameters/bbw Band-pass averaged backscattering coefficient for seawater m^-1 float32 -32767 4.9999998736894E-6 to 1 N/A N/A
sensor_band_parameters/F0 Mean Solar Flux W m^-2 um^-1 float32 -32767 0 to 250 N/A N/A
sensor_band_parameters/k_no2 NO2 Absorption cross-sections cm^2 molecule^-1 float32 -32767 0 to 0.10000000149012 N/A N/A
sensor_band_parameters/k_oz Ozone Absorption cross-sections cm^-1 float32 -32767 0 to 0.10000000149012 N/A N/A
sensor_band_parameters/Tau_r Rayleigh Optical Thickness N/A float32 -32767 0 to 0.5 N/A N/A
sensor_band_parameters/vcal_gain Vicarious Calibration Gain N/A float32 -32767 0 to 2 N/A N/A
sensor_band_parameters/vcal_offset Vicarious Calibration Offset mW cm^-2 um^-1 sr^-1 float32 -32767 0 to 10 N/A N/A
sensor_band_parameters/wavelength wavelengths nm int32 -32767 0 to 20000 N/A N/A
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