Specifications

56
5.7.2.4 Spectral parameters (MsgID = 3)
Table 5.7.12 explains the "Spectral parameters" message. The periods T(n,n+1) := m
n
/m
n+1
and
T(n,n+2) := √(m
n
/m
n+2
) are computed from the moments m
n
of the spectrum.
∫
= )( fSfdfm
n
n
(5.7.9)
In addition, T
dw
and Goda’s peakedness parameter Q
p
are included:
)(
1
21
0
fSfdf
m
T
dw
∫
−
= (5.7.10)
∫
= )(
2
2
2
0
fSfdf
m
Q
p
(5.7.11)
plus the peak period T
p
, defined through S(1/T
p
) = S
max
. See also Table 5.7.17. Other parameters,
such as the bandwidth parameters
ε and ν , or the significant steepness S
s
, can be computed from
the periods in the message:
1
2
1
−
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
=
z
T
T
ν
(5.7.12)
2
1
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
−=
z
c
T
T
ε
(5.7.13)
2
0
/2
zms
gTHS π = (5.7.14)
Table 5.7.12. Spectral parameters message (MsgID = 3).
Byte HiNibble LoNibble
0 MsgID = 3 = 0011 CRC-4 checksum
1 √m
0
2 T
I
= T(−2,0)
3 T
E
= T(−1,0)
4 T
1
= T(0,1)
5 T
z
= T(0,2)
6 T
3
= T(1,3)
7 T
c
= T(2,4)
8 T
dw
9 T
p
10 1/Q
p
5.7.2.5 Buoy information (system file) (MsgID = 5)
Table 5.7.13 explains the "Buoy information" message. The GPS position is a 24-bit Latitude
and a 24-bit Longitude. Both are two's-complement values. Positive values are North (East),
negative values are South (West). The scaling is:
23
321
2/)1000100000(90 ixixiLat
o
+⋅+⋅⋅= (5.7.15)
23
654
2/)1000100000(180 ixixiLon
o
+⋅+⋅⋅= (5.7.16)
The battery status is the battery life expectancy, i.e. the number of weeks that the battery cells
are expected to last. All three accelerometer offsets are 4-bit numbers, scaled linearly: A = i/8 in
units of m/s^2.