48 
implementation Panel Charter 
® Develop a complete system concept meeting 
user requirements. 
® Establish system feasibility. 
® Negotiate with user groups to arrive at a base- 
line system concept. 
® Quantify the performance of the baseline sys- 
tem. 
The end-to-end definition of a spaceborne 
remote sensing system encompasses a wide va- 
riety of topics including: 
® Sensor Definition - What type of instrument is 
required to perform these missions, and what 
are its specific design and performance char- 
acteristics? 
© Spacecraft Integration - How will this sensor be 
accommodated on the spacecraft in terms of 
its mass, power, and viewing requirements? 
On-board Data Handling - How will the data 
stream from the instrument be processed and 
stored on the spacecraft? 
® Data Downlink Formatting - How will the sen- 
sor's data be formatted, and what are the spe- 
cifics of the radio frequency channels for data 
transmission? 
Ground Reception and Processing - How and 
where will the downlinked data be received 
and processed? 
® Data Product Definition - What are the specific 
end products to be derived from the data 
stream, and how will they be formatted? 
® Data Access and Distribution - How and how 
soon after reception can the data be accessed 
and how and in what form will the data proa- 
ucts be distributed? 
Algorithm Development - What software tools 
are required to produce useful output data 
products from the raw data? Who will develop 
these tools, and how will these tools be made 
available to users? 
These and other issues were addressed by 
the Implementation Panel during the working 
sessions in February and April 1987. The results 
are discussed in some detail in the balance of this 
section. 
Sensor Definition 
Design Tradeoffs 
Usually a sensor concept is developed by 
performing tradeoffs among instrument perfor- 
mance characteristics, e.g., spatial, spectral, tem- 
poral, and radiometric resolution. However, in 
evolving the SeaWiFS design concept, many of 
the degrees of freedom normally available have 
already been constrained by spacecraft and 
data-format considerations. In addition, the high 
level of performance required of the sensor re- 
stricts the remaining design options. 
First of all, the resources of the Landsat-6 
spacecraft must be assumed to be principally 
dedicated to supporting the Enhanced Thematic 
Mapper (ETM) mission. Hence, the SeaWiFS in- 
strument must be lightweight and require little 
power. Also, the current launch schedule for 
Landsat-6 (4th quarter of 1990) limits the Sea- 
WiFS sensor design and fabrication efforts to an 
activity of about 20 to 24 months. This latter con- 
straint leads to the requirement for an uncompli- 
cated, proven-technology concept. Secondly, to 
minimize ground station requirements for users of 
SeaWiFS data, the SeaWiFS data product should 
be compatible with the AVHRR High-Resolution 
Picture Transmission (HRPT) format, for which 
there are many existing ground stations. 
Since HRPT is formatted into six frames of 
data per second, the best choice of line rate for 
SeaWiFS is equal to this frame rate. At an orbital 
altitude of 705 km, this immediately defines the 
sensor ground sampling distance (GSD). That is, 
the satellite's orbital velocity moves it 1.13 km 
over the ground in 1/6 second; therefore, suc- 
cessive scan lines will be 1.13 km apart on the 
ground at nadir. Since data-processing require- 
ments are eased when data are sampled in a 
square grid (equal angular sample spacing along 
