Temperature-Induced Bias Variations of Multi-Frequency Receivers

Precise GNSS applications, like PPP or RTK, make use of pseudorange and carrier-phase data. Traditionally, the ionospheric delays are removed to first order by using dual-frequency data. More recently, three or more frequencies are available from modernized and newly emerged systems. Most observation models assume the inter-signal biases for pseudoranges and carrierphases to be time-invariant. A violation of this assumption may be uncritical for dual-frequency processing in many cases, but with three frequencies the variations are not absorbed any more by nuisance parameters and may affect actual estimation parameters of interest. Coping with variable receiver biases is essential for many GNSS applications particularly for high-precision positioning where fast ambiguity resolution relies on the use of triple-frequency observations. This study demonstrates the effects of temperature-dependent receiver bias variations for dual-frequency and triple-frequency data. Real tracking data from geodetic receivers is used together with simulated observations. The bias variations are studied using measurement residuals from positioning solutions as well as triple-frequency signal combinations. Possible means of mitigating the variations through adaptions of the estimation parameters as well as changes in receiver operation are shown

The ACES GNSS Subsystem and its Potential for Radio-Occultation and Reflectometry from the International Space Station

The ESA mission Atomic Clock Ensemble in Space (ACES) will operate a new generation of ultra-stable and accurate atomic clocks on board the International Space Station in 2013-2015. The ACES payload will be attached externally to the European Columbus module. A commercial-of-the-shelf GNSS receiver will be connected to the ACES clock signal. Primarily, the receiver will ensure orbit determination of the ACES clocks in order to apply relativistic corrections to the space-to-ground comparison between the ACES clock signal and the ground clock. Secondarily, the receiver offers the potential for remote sensing from space in the field of radio-occultation and reflectometry exploring the use of the new GNSS signals. The paper presents the current status of the ACES GNSS instrument

The ACES GNSS Remote Sensing Concept and Status of the GNSS Subsystem

Atomic Clock Ensemble in Space (ACES) is an ESA mission in fundamental physics based on a new generation of ultra-stable and accurate clocks operated in the microgravity environment of the International Space Station. A dedicated GNSS receiver on-board the ACES payload will ensure orbit determination of the ACES clocks in order to apply relativistic corrections to the space-to-ground comparison between the ACES clock signal and the ground clock. Furthermore, the ACES mission is exploiting remote sensing applications including high-rate radio-occultation and reflectometry data recordings arising from GPS L1, L2, L2C, L5 and GALILEO/GIOVE E1, E5a signals. In parallel to ACES continuous precise orbit determination measurements several daily radio-occultation and reflectometry measurements can be scheduled. The ACES GNSS remote sensing concept and status of GNSS subsystem will be presented in this paper

Detection of Arctic Ocean tides using interferometric GNSS-R signals

This paper evaluates the usage of reflected GPS signals for Earth observations to study changes of sea level and sea-ice in remote sensing. In a coastal setup, ∼670 m above Disko Bay (Greenland), signals with different carriers L1 and L2 were recorded. A method is presented that analyses the interferometric phase between the reflected and the direct signals and derives the height of the reflecting surface. The analysis includes a ray tracing and an estimation of signal coherence. It is shown that coherent reflections are related to sea-ice coverage. Absolute heights are derived with a time interval of ∼30 min. The altimetric results show semidiurnal tides that are validated using the AODTM-5 tide model. The residual height has a mean of 9.7 cm for L1 and 22.9 cm for L2. The dispersion is not significant but a significant tropospheric bias is detected with an error of up to 20 cm.Peer reviewe