mission specific


Instrument Overview

The Telltale wind indicator on PHX is a mechanical anemometer designed to operate on the Martian surface as part of the meteorological package on the NASA Phoenix lander. It consists of a lightweight cylinder suspended by Kevlar fibers and is deflected under the action of wind. Imaging of the Telltale deflection with the SSI allows the wind speed and direction to be quantified [GUNNLAUGSSON2008, TAYLORETAL2008].

Wind measurements were made with a frequency determined by how frequently the SSI could take images (down to once every 50 seconds).

Platform Mounting Description

The Telltale is mounted on top of the meteorological mast at roughly 2 metres height above the surface.

Principal Investigator

The Telltale was designed at constructed at Aarhus University in Denmark. Project leader is H. P. Gunnlaugsson. H. P. Gunnlaugsson and C. Holstein-Rathlou of the Atmospheric Theme Group (ASTG) led the data taking and data reduction efforts.

Scientific Objectives

The Telltale was designed to be capable of measuring wind speed in two horizontal components: perpendicularly to the SSI camera line-of-sight over the range 1-10 m/s with accuracy of 1 m/s for winds of 1 to 5 m/s and of 20% for winds of 5 to 10 m/s; and along the SSI camera line-of-sight over the range of 2 - 10 m/s with accuracy of 2 m/s for winds of 2 to 5 m/s and of 40% for winds of 5 to 10 m/s.

Operational Considerations

To fully reduce and utilize the data, pressure and temperature data are required, and the SSI would have to be able to take images of the instrument.


The Telltale was calibrated pre-flight at Aarhus University [HOLSTEIN-RATHLOU2008]. Final parameters of the calibration may change slightly upon complete analysis of the whole dataset. This effort is expected to be known early 2009.