Expressing 2D Gabor transform as 1D spectrum
Equation 11.1 shows the equation for $A$:
$$A(\tau,\omega) = A_0 \exp\left(-\frac{\omega \tau}{2Q}\right)$$

We see that $A$ really only depends on the product of $\tau$ and $\omega$, therefore by defining a new variable $\chi = \omega \tau$ we can rewrite this expression as

$$A(\chi) = A_0 \exp\left(-\frac{\chi}{2Q}\right)$$

Perhaps this helps.