## 1 Introduction  
Satellite remote sensing instruments operating in the infrared (IR) and microwave (MW) regions of the electromagnetic (EM) spectrum provide key information for global numerical weather prediction (NWP) models. Currently, more than 90% of all observational data assimilated in global NWP systems comes from satellites. When considering satellite observations only, the MW and IR sounders together make up about 79% of the positive impact of all satellite observations; 45% is from MW soundings and the other 34% from IR soundings [1; 2]. Major contributors to the reduction of forecast errors from temperature soundings are the Advanced Microwave Sounding Unit-A (AMSU-A - on board several platforms) and the Infrared Atmospheric Sounding Interferometer (IASI) hyperspectral instrument on board Meteorological Operational (MetOp) satellites [3; 4; 5; 6; 7; 8; 9]. For water vapour retrieval, currently one of the most informative satellite radiometers for humidity soundings is the Advanced Microwave Sounding Unit-B/Microwave Humidity Sounder (AMSU-B/MHS). The remote sensing data from these IR and MW instruments are useful for the retrieval of atmospheric temperature and water vapour vertical profiles [10; 11] and other atmospheric parameters. However, all of these instruments have drawbacks. Retrievals from IR hyperspectral instruments such as the IASI are considered to be of high quality. But these observations are restricted to clear sky conditions. The MW instruments can see down into clouds, and therefore provide important information about the atmospheric state and hydrometeors (rain, ice etc. ), and they are also used for the retrieval of sea surface parameters (e.g. sea surface temperature [12]). But the vertical resolution is very poor, due to the very limited number of sounding channels. The radiometric noise in these channels is also a limitation on performance. In future, it can be expected that there will be an increase in the number of satellite microwave sounding instruments, covering a wide range of applications including NWP (MicroWave Sounder (MWS) [13], MicroWave Imager (MWI) [13; 14]), climatology (Ice Cloud Imager (ICI) [13; 14]), precipitation monitoring and severe weather events (Geostationary Observatory for Microwave Atmospheric Sounding (GOMAS) [15]). Furthermore, recent technological advancements in MW sensors and instrumentation has paved the way for the development of new and advanced satellite MW remote sensing instrument concepts. An example of one such technology advancement is the development of on-chip superconducting filterbank spectrometers. This state-of-the-art technology will enable hundreds of spectral channels in the MW region, with individually tailored bandwidths, and resolution (v/\(\Delta\
u\)) greater than \(\sim\)1000, sensed down to the photon-noise limit [16]. Superconducting filterbank spectrometers differ from \"conventional\" heterodyne-based solutions in three main ways. Firstly, there is no down conversion stage; both the filters and power detectors operate at the signal frequency. Secondly, both the filterbank and detectors are implemented using superconducting technologies. Thirdly and importantly, the filterbanks and detectors are integrated together on the same device chip. The basic concept is illustrated in Figure 1.  
Figure 1: Schematic of a superconducting filterbank based on transition-edge superconducting detector technology. (**a**) Overall filterbank architecture. (**b**) Schematic of filterbank—half-wave resonator coupled to feedline and TES detector. (**c**) Prototype 10-channel low spectral resoluition (\(R\)=200) device chip. (**d**) Modelled filter response (\(R\)=200). Figures from Thomas et al. [16]. The signal from the observed scene is coupled via a broadband antenna to a mm-wave microstrip feed line. Half-wave resonator filters are capacitively coupled to the microstrip feed line and to a transition edge superconducting (TES) detector.