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FIGURE 4.1 The launch sequence of past, current, and planned ocean color sensors in polar orbit are displayed. The sensors still operational are shown with a one-sided arrow; the hatched area indicates when a sensor is beyond its design life. The gray shaded background indicates a data gap in the past and a potential data gap arising if MODIS sensors and MERIS cease today. The question marks are used to indicate sensors that either do not yet meet the minimum requirements or are vulnerable to changes in funding allocation. Future sensors are shown having either a five- or seven-year lifetime, according to their individual specifications. CZCS: Coastal Zone Color Scanner; OCTS: Ocean Color and Temperature Scanner; SeaWiFS: Sea-viewing Wide Field-of-view Sensor; OCM/OCM-2: Ocean Colour Monitor; MODIS-Terra/MODIS-Aqua: Moderate Resolution Imaging Spectroradiometer on Terra/Aqua, respectively; MERIS: Medium Resolution Imaging Spectrometer; GLI: Global Imager; VIIRS: Visible Infrared Imager Radiometer Suite; OLCI: Ocean Land Colour Instrument onboard Sentinel-3; PACE: Pre-Aerosol-Clouds-Ecosystem; GCOM-C: Global Change Observation Mission for Climate Research; JPSS: Joint Polar Satellite System.
SOURCE: Based on data from http://www.ioccg.org/sensors_ioccg.html.

TABLE 4.1 Current Sensors in Space Having Spectral Bands and Other Specifications That Provide Typea 1 or 2 Ocean Color Sensor Capabilities

Sensor/Satellite/Type Agency Launch Date Swath (km) Spatial Resolutionb (m) Bands (visible/total) Spectral Coverage (nm)
MODIS/Terra/1 NASA (USA) 1999 2,330 250/500/1,000 9/36 405-14,385
OCM-1/IRS-P4/2 ISRO (India) 1999 1,420 360/4,000 7/8 412-885
MERIS/2 ESA (Europe) 2002 1,150 300/1,200 12/15 412-1,050
MODIS/Aqua/1 NASA (USA) 2002 2,330 250/500/1,000 9/36 405-14,385
OCM-2/Oceansat2/2 ISRO (India) 2009 1,420 360/4,000 7/9 400-900

Listed in ascending order of launch date (for details see Appendix A).

a Sensors are characterized into Type 1-4 based on their spatial and spectral coverage and orbit (see Table 2.1).

b The sensor has some capability to sample at higher spatial resolution.

Conclusion: U.S. research and operational users of satellite ocean color data will have to rely on multiple sources, including sensors operated by non-U.S. space agencies, because the United States does not have approved missions that will sustain optimal ocean color data for all applications.

ANALYSIS OF CAPABILITIES AND GAPS

Our analysis of current and future capabilities is focused on the Type 1 and 2 sensors listed in Table 4.2 (those capable of providing global coverage approximately every two to three days), because most of the past experience is limited to



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