STPSat-1Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER)

The Spatial Heterodyne Imager for Mesospheric Radicals (SHIMMER) was the primary payload on STPSat-1, the first mini satellite for the Department of Defense (DoD) Space Test Program (STP). SHIMMER measured the UV emission between about 30 and 100 km altitude and 307.9 - 309.4 nm by imaging the limb with an altitude sampling of about 2.2 km. The high spectral resolution of 120 mÅ allowed the removal of the scattered solar background from the spectra leaving the mesospheric hydroxyl (OH) resonance fluorescence from which OH vertical density profiles could be inferred. OH remains one of the least measured trace gases in the middle atmosphere. This method was pioneered by NRL's MAHRSI (Middle Atmospheric High Resolution Spectrograph Investigation) instrument on space shuttle missions in the 1990s. Compared to MAHRSI, SHIMMER was not only smaller by a factor of three in mass and volume, but it sampled the atmosphere seven times faster due to its higher sensitivity. One additional goal of SHIMMER was to observe the equatorward edge of the polar mesospheric cloud (PMC) region, around 55 deg latitude. Originally, PMCs were thought to be caused solely by water vapor lofted from the lower atmosphere over the summer polar region. However, MAHRSI demonstrated that water vapor exhaust injected into the upper atmosphere from the space shuttle can also form PMCs. By observing both the OH (water vapor) and the PMCs, SHIMMER results helped quantify this contribution to PMCs.

SHIMMER（中气层自由基空间杂波成像仪）作为STPSat-1（国防部空间测试计划STP的首颗微型卫星）的主要有效载荷。该设备通过成像边缘，以约2.2公里的高度采样率，测量了大约30至100公里海拔高度和307.9至309.4纳米波长的紫外辐射。其高光谱分辨率达120毫埃，能够从光谱中去除散射的太阳背景，从而获得中气层羟基（OH）共振荧光，并由此推断出OH的垂直密度分布。OH作为中高层大气中最少被测量的痕量气体之一，其测量方法在20世纪90年代由NRL的MAHRSI（中气层高分辨率光谱仪调查）仪器在航天飞机任务中首创。与MAHRSI相比，SHIMMER在质量和体积上缩小了三倍，并且由于灵敏度更高，大气采样速度提高了七倍。SHIMMER的另一个目标是观测极地中气层云（PMC）区域的赤道边缘，大约位于55度纬度。最初，人们认为PMC仅由夏季极地地区从低层大气中升腾的水汽引起。然而，MAHRSI的研究表明，从航天飞机注入到高层大气的水汽排放也可以形成PMC。通过观测OH（水汽）和PMC，SHIMMER的结果有助于量化这种对PMC的贡献。