The thermospheric density and its variations are crucial to aerospace activities as well as space weather research and operation. However, due to the difficulties to observe the thermosphere, there has been a lack of effective descriptions for the overall general characteristics of thermospheric density. In this present paper, the Two-Line-Element datasets (TLEs) from multi-target low Earth orbit (LEO) satellites are used to derive a proxy of the daily average atmospheric density in the thermospheric shell located in the vicinity of LEOs’ orbital altitude. It captures the overall characteristics of the thermosphere and exhibits good correlations (0.84) with modeled and observed thermospheric density. By applying the spectral whitening method (SWM) to this proxy, a new index JsT is derived to describe non-periodic perturbation of the density where the specific satellite passed by. The fact that the JsT obtained from different satellites within the same thermospheric shell presents significant consistency to each other means that the new index is a good indicator for the overall feature of the variations of thermospheric density, and it is possible to define a unified regional index JrT to describe density disturbances for the thermospheric shell where these satellites flying through. Moreover, the JrT at different altitudes also present good consistency suggesting the possibility of defining a global index JpT, capable of describing the density variation of the entire thermosphere.