NOAA data compression using a multi length DPCM code and a variable length code NOAA data compression using a multi length DPCM code and a variable length code
AVHRR data
- Entropy
First of all we have examined the entropies of each channels fig.1 shows the entropies of the original channel data and their fluctuation in a day. The entropies of the visible channels change from 0-90 to 8.971 reaching the maximum in the afternoon and almost zero in midnight .In in contrast with the visible channels IR channels show a satellite change this is because the visible channels are subjected to the solar reflectance's. The seasonal change of the entropies of the visible near and IR channel is rather moderate in the comparison with their daily change.
- Correlation of channel
Fig 2 Shows the correlation coefficients between adjacent pixels of the original channel .the correlation of the horizontal direction in larger than the vertical one because the earth
Figure 2 the correlation coefficients between adjacent pixels
| CH-1,CH-2 |
Ch-2, CH-3 |
CH-3, CH4 |
CH-4,Ch-5 |
CH-6,CH-7 |
| 0.983 |
0.392 |
0.731 |
0.998 |
0.797 |
Any direction table 2 shows the inter channel correlation coefficient of the corresponding pixels. The inter channel between CH-1 and CH-2 and that of CH-4 and CH5 mark very high value. This feature is useful to the inter channel prediction.
Predication
Generally speaking the data system has redundancy from one sample to the next and this fact enables prediction error coding. The prediction error is between adjacent pixels Ek.
Ek=Xj --- X'j
Where the variable X
j denotes the jth sample in data stream and X'
j denotes a predicted value of X
j shows four prediction methods we have examined four prediction methods. (1) (2) (3) (4) and (5) for the example only X
j-1 contributed to the prediction process. Formula (1) (2) and (3) are used to the prediction in a channel. Formula (4) and (5) are used to the prediction between channels.
| (1) |
X'j = C |
|
:Previous prediction |
| (2) |
X'j = (C+B)%2 |
|
:Average prediction |
| (3) |
X'j = C - A + B |
|
:Panel prediction |
| (4) |
X'j = b |
|
:Inter channel prediction |
| (5) |
X'j = c - a + b |
|
:Inter channel prediction |
Where A, B, C a, b, c are reference pixels.
Table 3 shows the entropies by the each predictions .the entropies original image is very large. In the intra channel prediction. Prediction (1) is the smallest of the others (Average prediction) (2) and panel prediction (3) and in the inter channel prediction (5) is the smaller entropies the (4) since the variance of the prediction error (5) is smaller than the those of (4) inter channel prediction (5)is the smallest the total entropy of the others selecting CH-1 CH3 Ch-4 of the previous prediction and CH1,2 and Ch-4,5 of the inter channel prediction (5).
Figure 3: Prediction method
Table 3: The entropies by the prediction methods
| |
CH-1 |
CH-2 |
CH-3 |
CH-4 |
CH-5 |
Total entropy |
| Entropy |
7.876 |
7.903 |
8.937 |
8.387 |
8.437 |
41.540 |
| (1) |
5.705 |
5.721 |
6.240 |
4.611 |
4.759 |
27.036 |
| (2) |
5.839 |
5.879 |
6.330 |
4.744 |
4.893 |
27.685 |
| (3) |
6.456 |
6.474 |
6.977 |
5.354 |
5.513 |
30.774 |
| |
CH-1,2 |
CH-2,3 |
CH-3,4 |
Ch-4,5 |
CH-5,1 |
Total entropy |
| (4) |
5.967 |
9.422 |
4.747 |
8.278 |
37.408 |
8.993 |
| (5) |
3.288 |
6.779 |
6.305 |
3.172 |
5.544 |
25.088 |
