Das Projekt "Sonnenstrahlungsvariabilitaet, Oszillationen und Helioseismologie" wird vom Umweltbundesamt gefördert und von Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD,WRC) durchgeführt. The main objective is the determination of the variability of solar irradiance and the observation of solar oscillations for helioseismology. This, in order to document recent changes for climate related investigations and to improve our knowledge and understanding of the physical mechanisms yielding the changes. Such understanding is needed to assess possible influences of the solar forcing on the Earth's climate in the past and future. To achieve this goal balloon and space experiments are designed, built and flown. The experiment SOVA (Solar Variability) is presently in space (launched August 1992) on the European platform EURECA. IPHIR (Interplanetary Helioseismology by Irradiance Measurements) was launched in July 1988 on the Russian mission PHOBOS to Mars. Major parts of the IPHIR and SOVA experiments (sunphotometers, radiometers, solar pointing monitors and the analog data acquisition) have been built by PMOD/WRC; IPHIR (C Froehlich as PI) in co-operation with Institut d'Astrophysique Spatiale, Orsay, F, the Space Science Department (SSD) of ESA and the Crimean Astrophysical Observatory; SOVA with the Institut Royale Meteorologique de Belgique (IRMB, D Crommelynck as PI) and the SSD. VIRGO, the most recent space experiment presently built, is a co-operation among SSD, IRMB, Instituto Astrofysica de Canarias and Observatoire de la Cote d'Azur, Nice, F, and is lead by PMOD/WRC (C Froehlich as PI). It will fly on the ESA/NASA SOHO mission (launch in fall 1995). These space experiments are supplemented by irregular SIMBA (Solar Irradiance Monitoring from Baloons) flights in co-operation with Observatory of Geneva; the last flight took place from Air-sur-l'Adours, F, in September 1992 and the next is planned for June 1994.