42 
30°, and qualitative observations of color fea- 
tures are possible at larger angles, depending on 
atmospheric conditions. In a like manner, the ac- 
curacy of sea-surface temperature measure- 
ments decreases as the amount of water-vapor 
absorption increases due to slant path viewing. 
Therefore, the scientific community was satisfied 
with 2-day coverage (45° scan). However, since 
the commercial and operational users needed 
daily coverage and since providing daily revisit 
would not interfere with use of the data for re- 
search purposes, the Research Panel agreed 
that daily coverage should be a baseline Sea- 
WIFS requirement. 
Scan Plane Tilt 
Over the oceans, the data from a nadir view 
is contaminated by specular reflections from the 
oceans’ surface (sun glint). In order to minimize 
this effect, the field of view must be pointable on 
command along track to 20° on either side of na- 
dir, in addition to nadir (0°). Rapid slewing along 
track is desirable to minimize the loss of data. 
Calibration 
The research users expressed the absolute 
radiometric calibration accuracy goals for the 
SeaWiFS instrument as follows: When the instru- 
ment receives radiance levels from zero to the 
maximum level at its entrance aperture from a 
traceable (National Bureau of Standards) source, 
the output will be convertible to a value that is 
within 2% of the maximum radiance from the 
source for all reflectance bands. The desire for 
a lunar view to monitor the instrument's stability 
was also expressed. 
For the thermal-emittance bands, a calibrated 
blackbody "standard" source should be used. 
The measurements in the thermal-emittance 
bands should give values that are within 1% of 
the maximum radiance from the source value, 
which should range from zero to the maximum 
level. Thermal calibration requires a minimum of 
two points, with three being desirable. A deep- 
space view serves as a zero-radiance reference, 
and two blackbodies, emitting at appropriate tem- 
peratures in the thermal range of the sensor, pro- 
vide the other two points. It is recommended 
that every effort be made to include two black- 
body sources in SeaWiFS. 
System Requirements 
Data Processing, Downlinks and 
Formats, and Dissemination 
Commercial and Operational Users' 
Requirements 
The spatial resolution, revisit interval, and ac- 
cess time recommended by the Commercial and 
Operational Users' Panel is summarized in Table 
4. These requirements are based on the panel 
members’ knowledge of the data products deliv- 
ered from the CZCS and the AVHRR. 
The Navy has established the Navy and Ma- 
rine Corps Specific Data Requirements for Atmo- 
spheric-Environmental Data Measurements from 
Satellites. Recently an ad hoc committee of the 
Navy Space Oceanography Science Working 
Group reevaluated this list to recommend new 
scientific research and development programs 
and projects that should be carried out over the 
next decade in order to ensure proper utilization 
of forthcoming satellite resources by the Navy 
(Mitchell 1987). Of these requirements, those 
that might be addressed by the SeaWiFS sensor 
or next-generation instruments are included in 
Table 4. 
As indicated in Table 4, most commercial and 
operational users need to receive data once a 
day within 24 hours or less of the time of acquisi- 
tion, and some applications require daily, real-time 
reception. Two major user groups for commer- 
cial and operational applications can be identi- 
fied, and the data downlinks required differ for 
each. 
The first and largest group consists of mer- 
chant, fishing, and naval fleets who require a di- 
rect, daily downlink of data on local conditions. 
Currently, the worldwide merchant fleet compris- 
es over 25,400 ships over 1000 gross tons, and 
there are 11,800 oceangoing fishing vessels. On 
the order of 400 naval vessels are types that 
would be useful to equip for reception of these 
data. The second user group represents the 
