bands. Assuming the baseline spectral bands 
agreed upon by the users’ panels and shown in 
Table 7, this split would occur between 675 nm 
and 745 nm (i.e., between bands 4 and 5). The 
VNIR bands are paired so that a minimum of 
dichroic splits and VNIR aft assemblies are need- 
ed; this requires two sets of five VNIR detectors 
(for TDI in each band) per aft assembly. Since 
this array of detectors extends along the scan di- 
rection, the field of view required of the optical 
system is 1.0° (11 IFOVs, as shown in the detec- 
tor layout in Figure 22). The remaining spectral 
split occurs between 510 nm and 555 nm 
(between bands 2 and 3). In each of the three 
VNIR aft assemblies, two VNIR bands are focused 
and detected. The VNIR detectors are photodi- 
ode/preamplifier hybrids. 
Since the hardware synchronization of the 
existing HRPT ground stations is fixed at 6 frames 
per second and 11,090 10-bit words per frame, 
the data frame structure shown in Table 8 was 
selected. This format provides the proper syn- 
chronization blocks for the hardware, while still 
transmitting all of the required data, and yields an 
effective data rate of 665 kbps. 
Sensor Performance 
Three key performance parameters were ex- 
amined: radiometric performance, modulation 
Table 7. 
ONOnAFEWNM— 
* 
*Blocked from 759 to 770 nm to minimize interference 
from the oxygen absorption band. 
transfer function (MTF), and polarization sensitivi- 
ty. For the radiometric performance estimates, 
the VNIR SNR was calculated, and the results are 
given in Table 9. For these SNRs, the sensor gain 
was chosen so that each band saturated at a ra- 
diance equivalent to the radiance from a turbid 
atmosphere with maximum water-leaving radianc- 
es. The signal radiances are typical of the maxi- 
mum radiances expected at a 45° scan angle. As 
shown, the SeaWiFS performance exceeds the 
goals in all six VNIR bands. In addition, since the 
sensor has a selectable gain (one of four values) 
prior to quantization, performance can be tailored 
to various expected signal levels. 
In the TIR region, the noise-equivalent tem- 
perature difference (NEAT) for a 300K scene was 
calculated, and Table 10 shows these results for 
various spectral-band pairs. These values are all 
well within the performance goal of 0.29K at 
300K set forth in Section 4. 
The MTF was calculated at the Nyquist angu- 
lar frequency of 0.313 cy/mrad. The results indi- 
cate that the VNIR MTF will be 0.36 in the scan 
direction and 0.57 in the track direction; TIR MTF 
will be 0.34 and 0.53 in the scan and track direc- 
tions, respectively. These values correlate well 
with the nominal rule for sensor design that the 
MTF should equal or exceed 0.3 at the Nyquist 
frequency. 
SeaWiFS Baseline Spectral Bands 
Band Band 
Low chlorophyll 
Other pigments 
Baseline chlorophyll 
Subsurface scattering 
Atmospheric correction 
Atmospheric correction 
Sea-surface temperature 
Sea-surface temperature 
IMPLEMENTATION PANEL 
53 
