# The Microwave Temperature and Humidity Profiler: Description and Preliminary Results
## 2 Instrument Description
### Receivers Characterization: Noise Equivalent Temperature  
MTHP noise-equivalent temperature measurements were performed on the output of the IF chain (after down-conversion and before digitization) on both 60 GHz and 183 GHz channels. The system noise temperature test is performed using a 77 K liquid nitrogen-filled tank with an RF absorbent (see Figure 6). The antenna is pointed inside the tank and power measurements are performed using a calibrated power meter at each channel. After that, the antenna is pointed to an ambient temperature calibration load at 293 K. The Y-factor is measured, in dB, by subtracting the power value at ambient to the cold target measured power. The results of the receiver's Y-factor and noise-equivalent temperature (NET) estimates are provided in Table 1.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency**} & \multicolumn{2}{c}{**60 GHz**} & \multicolumn{4}{c}{**183 GHz**} \\ \cline{2-7}  & **51–55 GHz** & **55–59 GHz** & **183 GHz** & **182.8 GHz** & **182.6 GHz** & **179 GHz** \\ \hline
**Power measurement @ 293 K** & \(-14.75\) & \(-16.30\) & \(-21.24\) & \(-20.99\) & \(-21.60\) & \(-23.68\) \\
**[dB]** & \(-16.04\) & \(-17.60\) & \(-21.98\) & \(-21.76\) & \(-22.37\) & \(-24.39\) \\ \hline
**Y-factor [dB]** & \(1.29\) & \(1.30\) & \(0.78\) & \(0.74\) & \(0.77\) & \(0.77\) \\ \hline
**Receiver** & \(535.9\) & \(530.4\) & \(1066.6\) & \(1018.0\) & \(1018.0\) & \(1119.3\) \\
**Temperature [K]** & \(535.9\) & \(530.4\) & \(1066.6\) & \(1018.0\) & \(1018.0\) & \(1119.3\) \\ \hline \hline \end{tabular}
\end{table}
Table 1: MTHP measured Y-factor and noise-equivalent temperature calculations.  
Figure 5: Block diagram of the MTHP 183 GHz channel receiver.  
Given these receiver temperatures, we can estimate the single-channel Noise-Equivalent Temperature Difference (NETD) at 10 ms integration time as ([22], chapter 7):  
\[NETD=\frac{T_{Ant}+T_{Recv}}{\sqrt{B_{N_{eq}}\cdot\tau}},\]  
where \(B_{N_{eq}}\) is the 3-dB noise equivalent bandwidth for a Hanning window of 1.363 times the spectral resolution (i.e., a channel is measured every 3.9 MHz, but the actual noise bandwidth is 5.3 MHz due to the filter roll-off) for the 60 GHz channel, and 250 MHz bins for the 183 MHz channel, with a maximum antenna temperature (\(T_{Ant}\)) of 300 K (temperature of the thermally controlled calibration load). The NETD assuming no gain fluctuations for MTHP at its native bandwidths and integration time is given in Table 2.  
Note that the high NETD for the oxygen channels can be improved using two strategies: Reducing the high spectral resolution (Original \(B_{N_{eq}}=5.6\) MHz) by averaging adjacent channels and averaging samples with adjacent angular measurement (Original Resolution = 2.5\({}^{\circ}\)). This is accomplished in post-processing, giving the end user the flexibility to trade spatial and frequency resolutions for NETD.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Channels**} & \multicolumn{3}{c}{**60 GHz**} & \multicolumn{3}{c}{**183 GHz**} \\ \cline{2-7}  & **51–55 GHz** & **55–59 GHz** & **183 GHz** & **182.8 GHz** & **182.6 GHz** & **179 GHz** \\ \hline NETD [K] & 3.63 & 3.60 & 0.89 & 0.83 & 0.83 & 0.86 \\ \hline \hline \end{tabular}
\end{table}
Table 2: NETD estimations for the MTHP receiver.  
Figure 6: MTHP rotor while on the Y-factor measurement using a liquid nitrogen-filled tank with RF absorbent.