function [anoise] = AccelNoise(N1, delta)

% accel noise spectrum from Armstrong and Tinto

anoise = randn(N1, 1); 
anoise = fft (anoise);

df = (1/(N1*delta)); 

for k1 = 2:(N1/2) + 1
    fk = (k1-1)*df; 
    
    tf = sqrt(2.5/6)*(10^(-24))/fk;
    
    anoise(k1) = tf * anoise(k1);
end

anoise(1) = anoise(1)*(10^(-16)) * sqrt(2.5/6); 

for k1 = (N1/2)+2: N1
    anoise(k1) = conj(anoise( N1 - k1 +2)); 
end

%imaginary part in the order of 10^-34, 
%real part 10^-19. imaginary part : computational artifact
anoise = real(ifft(anoise));