This passage is from Matthaeus 14:29 of the Latin Vulgate. I've included much of the surrounding text because the lack of punctuation makes it difficult for me to distinguish the sentence structure.
respondens autem Petrus dixit Domine si tu es iube me venire ad te super aquas 29 at ipse ait veni et descendens Petrus de navicula ambulabat super aquam ut veniret ad Iesum 30 videns vero ventum validum timuit et cum coepisset mergi clamavit dicens Domine salvum me fac 31 et continuo Iesus extendens manum adprehendit eum et ait illi modicae fidei quare dubitasti 32 et cum ascendissent in naviculam cessavit ventus 33 qui autem in navicula erant venerunt et adoraverunt eum dicentes vere Filius Dei es
This can be seen at: http://biblehub.com/vul/matthew/14.htm
Am I correct in determining that the word "ambulabat" is here used as a present participle in the imperfect sense?