NOAA Office of Satellite and Product Operations

Satellite Observations of Ocean Color

Ocean Color is the water hue due to the presence of tiny plants containing the pigment chlorophyll within phytoplankton and other oceanic particles such as sediments, and colored dissolved organic material (DOM). Phytoplankton consists of small, single-celled ocean plants which constitute the base of the oceanic food web and produce organic carbon through photosynthesis. The rate at which photosynthesis proceeds is known as primary productivity. Different types of phytoplankton that contains different concentrations of chlorophyll have the effect of changing the color of water to green hues from the deep blue of its pure state.

Satellite sensing of ocean color provides important information of chlorophyll and other oceanic particle concentrations. Ocean color observed by satellite sensors (e.g., MODIS/Aqua and VIIRS/NPP) is the radiance emanating from the ocean due to scattering by phytoplankton (e.g., chlorophyll), sediments, and DOM. The observation of ocean color reveals the variability in the distribution and concentration of phytoplankton and the extent of primary productivity, and therefore permits a quantum leap in our understanding of oceanographic processes from regional to global scales. Moreover, satellite observations provide the rapid, global coverage required for studies of ocean productivity worldwide and play an important role in the remote sensing of ocean color.


Satellite Instruments

Moderate-resolution Imaging Spectroradiometer (MODIS)

MODISThe Moderate-resolution Imaging Spectroradiometer (MODIS) is a instrument launched by NASA in 1999 on board the Terra (10:30 a.m.) satellite, and in 2002 on board the Aqua (1:30 p.m.) satellite. The instruments have 36 spectral bands ranging in wavelength from 0.4 to 14.4 µm and at varying spatial resolutions. It has 20 reflective solar bands from 410 nm to 2.1 µm and has 16 thermal emissive bands from 3.7 to 14.4 µm (see the tables).

Table 1. Moderate-resolution Imaging Spectroradiometer (MODIS) Instrument Specifications
(Reference: modis.gsfc.nasa.gov/about/specifications.php)

Orbit: 705 km, 10:30 a.m. descending node (Terra) or 1:30 p.m. ascending node (Aqua), sun-synchronous, near-polar, circular
Scan Rate: 20.3 rpm, cross track
Swath Dimensions: 2330 km (cross track) by 10 km (along track at nadir)
Telescope: 17.78 cm diam. off-axis, afocal (collimated), with intermediate field stop
Size: 1.0 x 1.6 x 1.0 m
Weight: 228.7 kg
Power: 162.5 W (single orbit average)
Data Rate: 10.6 Mbps (peak daytime); 6.1 Mbps (orbital average)
Quantization: 12 bits
Spatial Resolution: 250 m (bands 1-2)
500 m (bands 3-7)
1000 m (bands 8-36)
Design Life: 6 years
Table 2. MODIS Channel Specifications (Bands 1-19 are in nm; Bands 20-36 are in µm)
(Reference: modis.gsfc.nasa.gov/about/specifications.php)

Primary Use Band Bandwidth1 Spectral
Radiance2
Required
SNR3
Land/Cloud/Aerosols
Boundaries
1 620 - 670 21.8 128
2 841 - 876 24.7 201  
Land/Cloud/Aerosols
Properties
3 459 - 479 35.3 243
4 545 - 565 29.0 228
5 1230 - 1250 5.4 74
6 1628 - 1652 7.3 275
7 2105 - 2155 1.0 110
Ocean Color/
Phytoplankton/
Biogeochemistry
8 405 - 420 44.9 880
9 438 - 448 41.9 838
10 483 - 493 32.1 802
11 526 - 536 27.9 754
12 546 - 556 21.0 750
13 662 - 672 9.5 910
14 673 - 683 8.7 1087
15 743 - 753 10.2 586
16 862 - 877 6.2 516
Atmospheric
Water Vapor
17 890 - 920 10.0 167
18 931 - 941 3.6 57
19 915 - 965 15.0 250
Primary Use Band Bandwidth1 Spectral
Radiance2
Required
NE[delta]T(K)4
Surface/Cloud
Temperature
20 3.660 - 3.840 0.45(300K) 0.05
21 3.929 - 3.989 2.38(335K) 2.00
22 3.929 - 3.989 0.67(300K) 0.07
23 4.020 - 4.080 0.79(300K) 0.07
Atmospheric
Temperature
24 4.433 - 4.498 0.17(250K) 0.25
25 4.482 - 4.549 0.59(275K) 0.25
Cirrus Clouds
Water Vapor
26 1.360 - 1.390 6.00 150(SNR)
27 6.535 - 6.895 1.16(240K) 0.25
28 7.175 - 7.475 2.18(250K) 0.25
Cloud Properties 29 8.400 - 8.700 9.58(300K) 0.05
Ozone 30 9.580 - 9.880 3.69(250K) 0.25
Surface/Cloud
Temperature
31 10.780 - 11.280 9.55(300K) 0.05
32 11.770 - 12.270 8.94(300K) 0.05
Cloud Top
Altitude
33 13.185 - 13.485 4.52(260K) 0.25
34 13.485 - 13.785 3.76(250K) 0.25
35 13.785 - 14.085 3.11(240K) 0.25
36 14.085 - 14.385 2.08(220K) 0.35
1 Bands 1 to 19 are in nm; Bands 20 to 36 are in µm
2 Spectral Radiance values are (W/m2 -µm-sr)
3 SNR = Signal-to-noise ratio
4 NE(delta)T = Noise-equivalent temperature difference

Note: Performance goal is 30-40% better than required

Visible/Infrared Imager/Radiometer Suite (VIIRS)

VIIRSThe Visible/Infrared Imager/Radiometer Suite (VIIRS) is one of five instruments onboard National Polar-orbiting Partnership (NPP) and crosses the equator at about 1:30 p.m. local time (npp.gsfc.nasa.gov/viirs.html). The planned lifespan for the VIIRS is five years although its potential life expectancy could be seven years. The VIIRS builds on MODIS and AVHRR heritage and provides high radiometric accuracy and spatial resolution multispectral imagery. The instrument has 22 bands, i.e., 16 "Moderate" resolution (750 m) bands (M bands), 5 "Imagery" resolution (375 m) bands (I bands), and the low-light Day-Night-Band (750 m). Generally, the VIIRS can provide information about cloud, aerosols, ocean color, lake color, forest cover and productivity, sea ice coverage, etc.

Table 1. VIIRS 16 M-Band Information
(Reference: weather.msfc.nasa.gov/sport/jpsspg/viirs.html)


VIIRS 16 M-Band Information, please visit link to get more information

Okeanos Ocean Color Products
Ocean Color Products Statistics Analysis
Product Monitoring
Additional Information