  In this work, we aim to take a detailed experimental picture of the positive
streamer. We apply optical emission spectroscopy to the first negative system
(FNS, ${\rm B}^2\Sigma_{\rm u}^+\rightarrow {\rm X}^2\Sigma_{\rm g}^+$) of
N$_2^+$ and the second positive system (SPS, ${\rm C}^3\Pi_{\rm u}\rightarrow
{\rm B}^3\Pi_{\rm g}$) of N$_2$. Large, centimeter wide, and highly
reproducible streamers are created in pure nitrogen and synthetic air, at
pressures ranging from 33 to 266\,mbar. Direct time resolved spectral imaging
of the space charge layer resulted in spatiotemporal maps of the calculated
reduced electric field strength ($E/N$) and rovibrational temperature in
sub-nanosecond and sub-millimetre resolution. The $E/N$ peaks at approximately
540 and 480\,Td, directly in front of the space charge layer, for synthetic air
and pure nitrogen respectively, as determined by using the intensity ratio
method of FNS and SPS. A global model for pure nitrogen in PLASIMO uses the
experimentally determined $E/N$ distribution to draw a picture of the gas
kinetics around the space charge layer passage. In addition, the results of the
global model serve as a reference to interpret the rotational and vibrational
temperatures obtained from experimental FNS and SPS emissions, which emphasize
the streamers' non-equilibrium gas heating.
