Performance of Saral/AltiKa over inland water - effects of atmospheric water content

Eva Börgens (Deutsches Geodätisches Forschungsinstitut (DGFI), Germany)


Christian Schwatke (DGFI, Germany); Denise Dettmering (DGFI, Germany)

Event: 2014 SARAL/AltiKa workshop

Session: Inland Waters (contributions involving specifically SARAL/AltiKa)

Presentation type: Type Poster

The Saral (Satellite with ARgos and AltiKa) mission launched in 2013 is the first altimeter satellite that carries a Ka-band instrument (AltiKa). The use of Ka-band has manifold advantages: one is the smaller footprint which allows a closer approach to the shoreline due to less disturbed waveforms and decreased hooking effect. This allows us, together with a higher spatial resolution caused by the 40Hz measurement frequency, to use the Saral/AltiKa data for monitoring smaller inland water bodies. However, a disadvantage is the stronger attenuation of the Ka-band due to atmospheric water content.

From theory, one expect already an impact of light rain on the Ka-band measurements, whereas heavy rain hardly effects the Ku-Band measurements. Not only rain but in general higher water content in the troposphere caused by clouds or fog can distort the waveforms. The distortion of the waveform can hinder the on board retracker to extract valid ranges. This is a most prominent problem, especially in the tropics where we have to expect rain and a high level humidity every day.

In this study, we investigate the ability of Saral/AltiKa for inland water level estimation. In particulary, we examine the influence of rain and clouds on the altimeter measurements. We analyze the waveforms and compare the derived water level heights with external data. For validation gauges as well as external weather information are used. Finally, we compare the weather dependence of AltiKa Ka-band measurements with those of the Envisat Ku-band measurements. Saral is flying in the same orbit as Envisat following a 35-day repeat cycle. Therefore, we are able to compare waveforms from Ka- and Ku-band measurements at the same location and with the same weather conditions which allows us to investigate the influence of the altimeter frequency on atmospheric attenuation as well as on closest approach to the coast and on hooking effects.
Eva Börgens
Deutsches Geodätisches Forschungsinstitut (DGFI)