clear all; close all;pack;
load grav_040700.dat;
load grav_040800.dat;
load grav_040900.dat;
grav_t=[
    grav_040700(:,3);
    grav_040800(:,3);
    grav_040900(:,3);
];
grav_dim=size(grav_t);
grav_dim_2=ceil(grav_dim(1,1)/2);
Fs=1/60;
size_in_sec=length(grav_t)/Fs;
time=(0:1/Fs:size_in_sec-1/Fs)';  %Time
%F=(0:1/size_in_sec:Fs)';

%N=2^nextpow2(size_in_sec)
N=2^nextpow2(grav_dim(1,1))
N_2=N/2;
F=Fs/2*linspace(0,1,N_2);
g_fft=fft(grav_t,N_2)/grav_dim(1,1);
grav_fft=abs(g_fft);
plot(time, grav_t)

figure
loglog(F,2*grav_fft);
grid on;
[Pxx, f]=pwelch(grav_t, [], [], N_2, Fs);
loglog(f,Pxx);