Y X Y

where 7} is the maximum look angle in radians, h is the orbit altitude, Vg is the spacecraft ground-track velocity, Sw is the swath width, X is the across-track pixel dimension, and Y is the along-track pixel dimension. The approximation is good for small swath widths. The data rate can be increased by transmission overhead such as housekeeping data or coding and it can be decreased by data compression. (See Sees. 2.1.1, 13.2.2, and 15.3.2.).

TABLE 9-15. Calculation Design Parameters for a Passive Optical Sensor.

Step

Calculation

FireSat

Comments

Step 1. Define Orbit Parameters

Define orbital altitude, h Design parametert

h = 700 km

See Table 3-4, Sec. 7.4

Compute orbit period, P Eq. (7-7), IRC

P= 98.8 mln

Assumes circular orbft

Compute ground track velocity, Vg

Eq. (5-31), IRC*

Vg = 6.76 km/s Assumes circular orbit

Compute node shift, AL

Eq. (7-13), IRC*

Ai = 24.8 deg

Function of Inclination

Step 2. Define Sensor Viewing Parameters

Compute angular radius of the Earth, p

Eq. (5-15), IRC*

p = 64.3 deg

Depends on orbital altitude

Compute max distance to the horizon, Dmax

Eq. (5-17), IRC*

3,069 km

Depends on orbital altitude

Define max. Incidence ang. M, or max. Earth cen. ang. ECA^

Design parameter, IRC*

IA = 70 deg

Adjust swath width for good coverage (Sec. 7.4)

Compute sensor look angle (= nadir angle), n

Eqs. (5-24) or (5-25b), IRC*

»1 = 57.9 deg

Will be less than p

Compute mln. elev. angle, e= 90°- IA

Eqs. (5-25b) and (5-28), IRC*

e=20 deg

If max. ECAmgx given, compute e

Compute max Earth central angle, ECA^

Eqs. (5-25b) and (5-26), IRC*

ECAmw(= 12.1 deg

If e given, compute ECAna*

Compute slant range, R§

Eq. (5-27), IRC*

f?s = 1,578 km

Rs here = Din Chap. 5

Find swath width

= 2 ECAmax

2 ECAmax= 24.2 deg

Determines coverage

Step 3. Define Pixel Parameters and Data Rate

Specify max. along-track ground sampling dlst, /ma*

Design parameter

Ymax= 68 m

Based on spatial resolution requirements atEGV,

Determine Instantaneous field of view, IFOV

¡rov _ Ynwx 180deg Rs n

IFOV= 0.00245 deg

One pixel width

Find max. cross-track pixel resolution, Xm^ at ECA^

0 0

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