The Humidity Sounder for Brazil (HSB) was an instrument launched on NASA's Earth Observing System satellite Aqua launched in May 2002. It was a four-channel passive microwave radiometer, with one channel at 150 GHz and three channels at 183 GHz. It was very similar in design to the AMSU-B instrument, except it lacked the 89 GHz surface sounding channel. It was intended to study profiles of atmospheric water vapor and provide improved input data to the cloud-clearing algorithms in the Unified AIRS Retrieval Suite, but the scan mirror motor failed on February 5, 2003. It worked with the Atmospheric Infrared Sounder and AMSU-A to form the AIRS Sounding Suite.
HSB was manufactured by Matra Marconi Space, Limited (MMS), in the United Kingdom under a contract with the Brazilian National Institute for Space Research (INPE).
Table 1: Radiometric characteristics of the HSB
| Channel Number | AMSU-B Channel Number | Frequency (GHz) | Bandwidth (at nadir) | Instrument Sensitivity NEDT (K) |
|---|---|---|---|---|
| 1 | 16 | 89.9 ± 0.9 | DELETED | DELETED |
| 2 | 17 | 150 ± 0.9 | 4000 | 0.68 |
| 3 | 18 | 183.31 ± 1.00 | 2x500 | 0.57 |
| 4 | 19 | 183.31 ± 3.00 | 2x1000 | 0.39 |
| 5 | 20 | 183.31 ± 7.00 | 2x2000 | 0.30 |
HSB stopped scanning suddenly and without warning over the Pacific Ocean February 5, 2003 at 21:39 UTC. The most likely cause is an electrical failure in the scan electronics. By design AMSU-B and therefore HSB had very limited hardware redundancy and software update capability.