The output unit of pwelch function

Hi,

I need to clarify the output unit of the function pwelch. The help says the output is psd. Could someone please help me clarify my understanding of the unit of this psd?

First about the function fft. Using the MatLab example:

...

NFFT = 2^nextpow2(L); % Next power of 2 from length of y

Y = fft(y,NFFT)/L;

...

effectively it is a DFT (right?). So:

1). If y has a velocity unit m/s, what should be the unit of 2*abs(Y(1:NFFT/2+1))? Is it (m/s)/Hz(=m) ?

2). If this is correct, then if I need a energy like output, then what I need is the term 2*(abs(Y(1:NFFT/2+1))).^2, am I right?

Now about the pwelch function:

Say I run the following command:

...

[pxx,f]=pwelch(y,hanning(segsz),ovp*segsz,segsz,Fs);

...

where segsz=NFFT/4 and Fs=1000 (1000Hz sample rate),

3) what is the unit of pxx? Is it (m/s)/Hz or (m/s)^2/Hz(=m^2/s)

Many thanks for your help!

Liam