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The solar wind transients propagating out in the inner heliosphere can beobserved in white-light images from Heliospheric Imager-1 (HI1), an instrumentof the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) onboard the Solar Terrestrial Relations Observatory (STEREO), from twoperspectives. The spatial velocity distribution inside solar wind transients iskey to understanding their dynamic evolution processes. We generated a velocitymap of transients in 3D space based on 2D white-light images and used it toestimate the expansion rate as well as some kinematic properties of solar windtransients. Based on the recently developed correlation-aided reconstruction(CORAR) method in our previous work, which can recognize and locate 3D solarwind transients from STEREO/HI1 image data, we further developped a newtechnique for deriving the spatial distribution of the radial velocities of themost pronounced features inside solar wind transients. The technique wasapplied to events including a coronal mass ejection (CME) and three small-scaletransients, so-called blobs, observed by HI1 on 3-4 April 2010 to reconstructtheir radial velocity maps. The results match the forward-modeling results,simulations, and in situ observations at $1$ AU fairly well. According to theobtained spatial distributions of height and radial velocity of the CME, weanalyzed the self-similarity of the radial expansion of the CME ejecta. Thedimensionless radial expansion rate of the northern and middle parts of the CMEejecta varies in the range of 0.7 - 1.0 at heliocentric distance between 25 Rsand 55Rs and the rate of the southern part in the range of 0.3 - 0.5,suggesting that the CME structure was distorted and shaped by the ambient solarwind. The technique we developed is expected to be applied to more events.

Radial velocity map of solar wind transients in the field of view of STEREO/HI1 on 3 and 4 April 2010