I am working with 16-day MODIS EVI (satellite) data and I want to fit a Piecewise Logistic Function through my 23 EVI data values. The following formula is for the Piecewise Logistic Function:
y(t) = (c / (1 + e^(a+bt))) + bEVI
where:y is the day of year
a is vegetation growth time
b is rate of leaf development
c is the amplitude
bEVI is the background EVI value [constant]
For some reason there is very little clarification about each component of the equation in most papers. I am assuming that the bEVI value is a constant but am supposing that one or two other components are constants too?
I have little experience with this function, but from the literature I have read, is applied separately to the left and then subsequently to the right of this bell-shaped curve - split at the maximum y value. I am hoping someone here with a stronger mathematical background and experience using the piecewise logistic function would be able to advise me on which component of the equation above should be a constant and which should be a variable.
The series of days of the year are as follows:1
17
33
49
65
81
97
113
129
145
161
177
193
209
225
241
257
273
289
305
321
337
353
Here is an example EVI dataset I currently have for one year of 23 data points:
0.425
0.3899
0.2417
0.4724
0.4648
0.226
0.245
0.2509
0.2741
0.3711
0.3914
0.3985
0.4433
0.397
0.3329
0.3578
0.2741
0.2912
0.3053
0.2995
0.0959
0.3287
-0.3
Would greatly appreciate any help at all. Thank you! =)
أكثر...
y(t) = (c / (1 + e^(a+bt))) + bEVI
where:y is the day of year
a is vegetation growth time
b is rate of leaf development
c is the amplitude
bEVI is the background EVI value [constant]
For some reason there is very little clarification about each component of the equation in most papers. I am assuming that the bEVI value is a constant but am supposing that one or two other components are constants too?
I have little experience with this function, but from the literature I have read, is applied separately to the left and then subsequently to the right of this bell-shaped curve - split at the maximum y value. I am hoping someone here with a stronger mathematical background and experience using the piecewise logistic function would be able to advise me on which component of the equation above should be a constant and which should be a variable.
The series of days of the year are as follows:1
17
33
49
65
81
97
113
129
145
161
177
193
209
225
241
257
273
289
305
321
337
353
Here is an example EVI dataset I currently have for one year of 23 data points:
0.425
0.3899
0.2417
0.4724
0.4648
0.226
0.245
0.2509
0.2741
0.3711
0.3914
0.3985
0.4433
0.397
0.3329
0.3578
0.2741
0.2912
0.3053
0.2995
0.0959
0.3287
-0.3
Would greatly appreciate any help at all. Thank you! =)
أكثر...