Profiles of radio refractive index and humidity derived from radar wind profilers and the Global Positioning System

Abstract

Abstract. It has often been pointed out that the Bragg backscatter of radar waves from elevated turbulent layers is very highly correlated with the height gradient of radio refractive index (RI) through these layers. However, many users need the profiles of RI, or the associated humidity, rather than profiles of their gradients. Simple integration of the gradients is usually not feasible because of ground or sea clutter and because biological scatterers such as insects and birds often severely contaminate the lower range gates. We show that if the total height-integrated RI is independently available (say, from the Global Positioning System (GPS)), and if the surface value of RI is known, the profiles of RI are retrievable with good accuracy. For those profiler systems equipped with a radio acoustic sounding system to measure temperature, the humidity is also retrievable.The method is demonstrated with data collected in southern California, where 7 hours of profiler data were recorded at 449 MHZ along with GPS data. Three radiosonde balloons were launched during the period, and the profiles of RI from the balloon and the profiler are compared. The advantages of the system are its invulnerability to nonprecipitating clouds (at frequencies of 449 MHZ or lower) and that it uses only facilities that will soon be deployed globally. Simulations are used to assess errors from various factors such as loss of sign of the gradient of the potential RI (important especially during some frontal events) and the presence of biological contaminants in some geographical areas (such as coastal zones and some agricultural areas at night). IntroductionThe close relationship between radio refractive index (RI) gradients with height and the distribution of Bragg backscattered power with height has been noted for decades; for example, see ] (hereinafter referred to as G98) we argued that a practical use for the profiler data was to assimilate the humidity gradient information into models. However, the new availability of temperature sounding by RASS and the imminent availability of global total precipitable water vapor (PWV) 371

Estimation of temperature and humidity from MST radar observations

“…This kind of discrepancy is also observed by several other investigators (Tsuda, 1997;Gossard et al, 1999). In spite of all these limitations, the agreement between the radar and radiosonde measured values of temperature and humidity shows the capability of the radar in deriving temperature and humidity.…”

“…Fourth, knowing the sign of M is not possible from the MST radar observations. Gossard et al (1999) stressed the importance of the sign of the potential refractive index gradients in retrieving the humidity profile. But in the present study, the sign of M is taken from simultaneous radiosonde measurements.…”

“…The same methodology is also used by Gossard et al (1999) to retrieve the profiles of the refractive index gradients, as well as humidity from the combined measurements of ground-based radar, RASS and Global Positioning Systems (GPS). But Tsuda (1997) proposed a technique to retrieve the humidity from the combined observations of radar and RASS.…”

Estimation of Humidity Profiles by Combining Co-Located VHF and UHF Wind-Profiling Radar Observation

“…Stankov et al (1996) first obtained humidity profile by using 449 MHz wind profiling radar measurements of turbulence echoes to constrain the MWR PWV observations within the statistical retrieval algorithm. Gossard et al (1999) obtained humidity profiles by constraining the sign of M from GPS-derived PWV. Stankov et al (2003) integrated the vertical gradient of the humidity profile obtained from 913 MHz and 449 MHz wind-profiling radar turbulence echo measurements to obtain boundary layer humidity profiles.…”

Estimation of Humidity Profiles with the L-Band Boundary Layer Radar-RASS Measurements

“…In order to monitor humidity profiles continuously, regardless of day or night, or weather conditions, a radar remote-sensing technique, to measure humidity profiles has been developed at NOAA (National Oceanic Atmospheric Administration) and Kyoto University, by using a 913 MHz BLR (e.g., Gossard et al 1998;Stankov et al 2003) and the MU radar on 46.5 MHz (e.g., Tsuda et al 2001;Furumoto et al 2003), respectively.…”